XR21V1410IL16TR-F - MaxLinear, Inc.

XR21V1410

1-CH FULL-SPEED USB UART

JUNE 2018 REV. 1.4.1

GENERAL DESCRIPTION

The XR21V1410 is an enhanced Universal

Asynchronous Receiver and Transmitter (UART) with

a USB interface. The USB interface is fully compliant

to Full Speed USB 2.0 specification that supports 12

Mbps USB data transfer rate. The USB interface also

supports USB suspend, resume and remote wakeup

operations.

The XR21V1410 operates from an internal 48MHz

clock therefore no external crystal/oscillator is

required as in previous generation UARTs. With the

fractional baud rate generator, any baud rate can

accurately be generated using the internal 48MHz

clock.

The large 128-byte TX FIFO and 384-byte RX FIFO

of the XR21V1410 helps to optimize the overall data

throughput for various applications. The automatic

transceiver direction control feature simplifies both

the hardware and software for half-duplex RS-485

applications. If required, the multidrop (9-bit) mode

with automatic half-duplex transceiver control feature

further simplifies typical multidrop RS-485

applications.

The XR21V1410 operates from a single 2.97 to 3.63

volt power supply and has 5V tolerant inputs. The

XR21V1410 is available in a 16-pin QFN package.

The XR21V1410 uses the native OS CDC-ACM

driver or a MaxLinear supplied custom driver.

MaxLinear provides WHQL/HCK-certified software

drivers for Windows XP, Vista, 7, 8, 8.1 and 10 as well

as software drivers for Windows CE, Linux and Mac

OS X. Full source code is available.

APPLICATIONS

Portable Appliances

External Converters (dongles)

Battery-Operated Devices

Cellular Data Devices

Factory Automation and Process Controls

Industrial applications

FEATURES

USB 2.0 Compliant, Full-Speed (12 Mbps)

■Supports USB suspend, resume and remote

wakeup operations

± 5 kV HBM ESD protection on USB data pins

± 2 kV HBM ESD protection on all other pins

Enhanced UART Features

■UART data rates up to 12 Mbps

■Fractional Baud Rate Generator

■128 byte TX FIFO

■384 byte RX FIFO

■7, 8 or 9 data bits

■1 or 2 stop bits

■Odd, even, mark, space, or no parity

■Automatic Hardware (RTS/CTS or DTR/DSR)

Flow Control

■Automatic Software (Xon/Xoff) Flow Control

■Multidrop mode

■Auto RS-485 Half-Duplex Control

■Half-Duplex mode

■Selectable GPIO or Modem I/O

Internal 48 MHz clock

Single 3.3V power supply

5V tolerant GPIO inputs

16-pin QFN package

Virtual COM Port WHQL certified drivers

■Windows XP, Vista, Win7 and Win8

■Windows CE 4.2, 5.0, 6.0, 7.0

■Linux

■Mac

FIGURE 1. XR21V1410 BLOCK DIAGRAM

USB Slave

Interface

128- byte

TX FIFO

GPIOs/

Modem IO

Internal

48MHz

Oscillator

USBD+

USBD-

384- byte

RX FIFO

GPIO5/RTS#/RS485

GPIO4/CTS#

GPIO3/DTR#

GPIO2/DSR#

GPIO1/CD#

GPIO0/RI#/RWK#

UART

Fractional

BRG

Internal

Status and

Control

Registers

3.3V VCC

GND

I2C

Interface

SDA

SCL

XR21V1410

1-CH FULL-SPEED USB UART REV. 1.4.1

FIGURE 2. PIN OUT ASSIGNMENT

16-Pin

QFN

GPIO5/RTS#/RS485

GPIO4/CTS#

LOWPOWER

GND

GPIO1/CD#

GPIO0/RI#/RWK#

GPIO2/DSR#

GPIO3/DTR#

16 15 14 13

USBD-

GND

USBD+

VCC

SDA

SCL

5678

ORDERING INFORMATION(1)

PART NUMBER OPERATING TEMPERATURE RANGE LEAD-FREE PACKAGE PACKAGING METHOD

XR21V1410IL16-F -40°C to +85°C Yes(2) 16-pin QFN Tray

XR21V1410IL16TR-F Tape and Reel

XR21V1410IL-0A-EB XR21V1410 Evaluation Board - RS-232 and RS-485 capable

XR21V1410IL-0B-EB XR21V1410 Evaluation Board - RS-232 capable

XR21V1410IL-0C-EB XR21V1410 Evaluation Board - RS-485 capable

NOTES:

1. Refer to www.exar.com/XR21V1410 for most up-to-date Ordering Information.

2. Visit www.exar.com for additional information on Environmental Rating.

XR21V1410

REV. 1.4.1 1-CH FULL-SPEED USB UART

PIN DESCRIPTIONS

NAME 16-QFN

PIN # TYPE DESCRIPTION

UART Signals

RX 10 IUART Channel A Receive Data. This pin has an internal pull-up resistor. 

Internal pull-up resistor is not disabled during suspend mode.

TX 9 O UART Channel A Transmit Data.

GPIO0/RI#/RWK# 8I/O General purpose I/O or UART Ring-Indicator input (active low) or Remote

Wakeup input. See “Section 1.5.13, Remote Wakeup” on page 11.

This pin has an internal pull-up resistor which is disabled during suspend

mode. If using this GPIO as an input, an external pull-up resistor is required to

minimize the device power consumption in the suspend mode.

GPIO1/CD# 7I/O General purpose I/O or UART Carrier-Detect input (active low). This pin has an

internal pull-up resistor which is disabled during suspend mode. If using this

GPIO as an input, an external pull-up resistor is required to minimize the

device power consumption in the suspend mode.

GPIO2/DSR# 6I/O General purpose I/O or UART Data-Set-Ready input (active low). 

See ”Section 1.5.6, Automatic DTR/DSR Hardware Flow Control” on page 9.

This pin has an internal pull-up resistor which is disabled during suspend

mode. If using this GPIO as an input, an external pull-up resistor is required to

minimize the device power consumption in the suspend mode.

GPIO3/DTR# 5I/O General purpose I/O or UART Data-Terminal-Ready output (active low). See

”Section 1.5.6, Automatic DTR/DSR Hardware Flow Control” on page 9.

This pin has an internal pull-up resistor which is disabled during suspend

mode. If using this GPIO as an input, an external pull-up resistor is required to

minimize the device power consumption in the suspend mode.

GPIO4/CTS# 4I/O General purpose I/O or UART Clear-to-Send input (active low). See ”Section

1.5.5, Automatic RTS/CTS Hardware Flow Control” on page 9.

This pin has an internal pull-up resistor which is disabled during suspend

mode. If using this GPIO as an input, an external pull-up resistor is required to

minimize the device power consumption in the suspend mode.

GPIO5/RTS#/RS485 3I/O General purpose I/O or UART Request-to-Send output (active low) or auto RS-

485 half-duplex control. See “Section 1.5.5, Automatic RTS/CTS Hardware

Flow Control” on page 9 or “Section 1.5.8, Auto RS-485 Half-Duplex Control”

on page 10. This pin has an internal pull-up resistor which is disabled during

suspend mode. If using this GPIO as an input, an external pull-up resistor is

required to minimize the device power consumption in the suspend mode.

USB Interface Signals

USBD+ 15 I/O USB port differential data plus. This pin has a 1.5 K Ohm internal pull-up.

USBD- 14 I/O USB port differential data minus.

XR21V1410

1-CH FULL-SPEED USB UART REV. 1.4.1

NOTE: Pin type: I=Input, O=Output, I/O= Input/output, OD=Output Open Drain.

I2C Interface Signals

SDA 11 I/O

OD I2C-controller data input/output (open-drain). An optional external I2C

EEPROM can be used to store default configurations upon power-up including

the USB Vendor ID and Device ID. See Table 3. A pull-up resistor (typically

4.7 to 10k Ohms) is required.

If an EEPROM is not used, this pin can be used with the SCL pin to select the

Remote Wake-up and Power modes. An external pull-up or pull-down resistor

is required. See Table 2

SCL 12 I/O

OD I2C-controller serial input clock. An optional external I2C EEPROM can be

used to store default configurations upon power-up including the USB Vendor

ID and Device ID. See Table 3. A pull-up resistor (typically 4.7 to 10k Ohms)

is required.

If an EEPROM is not used, this pin can be used with the SDA pin to select the

Remote Wake-up and Power modes. An external pull-up or pull-down resistor

is required. See Table 2

Miscellaneous Signals

LOWPOWER 2 O Low power status output. The LOWPOWER pin will be asserted whenever it is

not safe to draw the amount of current from VBUS power requested in the

Device Max Power field of the Configuration Descriptor. The LOWPOWER pin

will behave differently for a low power device and a high power device.

Low-power device (<= 1 unit load or 100 mA i.e. bMaxPower <= 0x32): LOW-

POWER pin is asserted when the USB UART is in suspend mode.

High-power deivce (bMaxPower > 0x32): LOWPOWER pin is

asserted when the USB UART is in suspend mode or when it is not yet

configured.

The LOWPOWER pin will be de-asserted whenever it is safe to draw the

amount of current requested in the Device Maximum Power field.

This pin is sampled momentarily at power-up or at any USB bus reset to 

configure the polarity of the LOWPOWER output during suspend mode. An

external (10K) pull-up resistor will cause the LOWPOWER pin to be asserted

HIGH during suspend mode. An external (3.3K) pull-down resistor will cause

the LOWPOWER pin to be asserted LOW during suspend mode.

Power / Ground Signals

VCC 16 Pwr +3.3V power supply.

GND 1, 13 Pwr Power supply common, ground.

GND Center

Pad

Pwr The center pad on the back side of the QFN package is metallic and should be

connected to GND on the PCB. The thermal pad size on the PCB should be

the approximate size of this center pad and should be solder mask defined.

The solder mask opening should be at least 0.0025" inwards from the edge of

the PCB thermal pad.

NAME 16-QFN

PIN # TYPE DESCRIPTION

XR21V1410

REV. 1.4.1 1-CH FULL-SPEED USB UART

1.0 FUNCTIONAL DESCRIPTIONS

1.1 USB interface

The USB interface of the XR21V1410 is compliant with the USB 2.0 Full-Speed Specifications. The USB

configuration model presented by the XR21V1410 to the device driver is compatible to the Abstract Control

Model of the USB Communication Device Class (CDC-ACM). The XR21V1410 uses the following set of

parameters:

1 Control Endpoint

■Endpoint 0 as outlined in the USB specifications

1 Configuration is supported

2 interfaces for the UART channel

■Single interrupt endpoint

■Bulk-in and bulk-out endpoints

1.1.1 USB Vendor ID

Exar’s USB Vendor ID is 0x04E2. This is the default Vendor ID that is used for the XR21V1410 unless a valid

EEPROM is present on the I2C interface signals. If a valid EEPROM is present, the Vendor ID from the

EEPROM will be used.

1.1.2 USB Product ID

The default USB Product ID for the XR21V1410 is 0x1410. If a valid EEPROM is present, the Product ID from

the EEPROM will be used. Note that Exar’s custom drivers for all Windows OS require that the Product ID be

an even number for the XR21V1410 device for proper identification of the device.

1.2 USB Device Driver

The XR21V1410 device can be used with either a standard CDC-ACM driver or a custom driver. When the

CDC-ACM driver is used, the driver has no capability to read or write the XR21V1410 device registers.

Because of this, the XR21V1410 device is initialized to the settings in Table 1. With a custom driver, all GPIOs

default in hardware to inputs but these settings may be modified by the custom driver.

TABLE 1: V1410 REGISTER DEFAULTS WITH CDC-ACM DRIVER

FLOW_CONTROL 0x01 Hardware flow control

GPIO_MODE 0x01 RTS / CTS flow control

GPIO_DIRECTION 0x08 GPIO3/DTR# configured as an output

GPIO_INT_MASK 0x30 GPIO0/RI#, GPIO1/CD# and GPIO2/DSR# are interrupt sensitive, i.e. can

cause a USB interrupt to be generated

Note also that when using a CDC-ACM driver, the XR21V1410 will automatically change the bMaxPacketSize

to 63 bytes to compensate for a known issue with the Microsoft CDC-ACM device driver. A register is available

to change this setting with a custom driver as well. See “Section 3.4.1, CUSTOM Register Description (Read/Write)”

on page 23. Although there is no ability to read / write registers when using the CDC-ACM driver, basic UART

functions, including setting baud rate, character format and sending line break are supported by the CDC

driver. Refer to the 4 CDC_ACM_IF USB Control Commands listed in Ta b l e 4, “Supported USB Control

Commands,” on page 12.

XR21V1410

1-CH FULL-SPEED USB UART REV. 1.4.1

1.3 I2C Interface

The I2C interface provides connectivity to an external I2C memory device (i.e. EEPROM) that can be read by

the XR21V1410 for configuration. If no external EEPROM is present, the SDA and SCL are used to specify

remote wakeup support and power mode as described in Table 2. These pins are sampled at power-up.

TABLE 2: REMOTE WAKEUP AND POWER MODES

SDA SCL REMOTE WAKE-UP

SUPPORT POWER MODE

1 1 No Self-Powered

1 0 No Bus-Powered

0 1 Yes Self-Powered

0 0 Yes Bus-Powered

1.3.1 EEPROM Contents

If SDA and SCL are both logic ’1’, the XR21V1410 device will first confirm if there is an external EEPROM

attached by attempting to read the first 8 locations of the ROM. If address 0x07 of the ROM contains the value

0x58 (as specified in Ta b l e 3), the contents of the ROM are assumed to be valid. Otherwise the EEPROM will

be ignored and the SDA / SCL bits are used to indicate remote wakeup support and device power mode.

The I2C address must be 0xA0. An EEPROM can be used to override default Vendor IDs and Device IDs, as

well as other attributes and maximum power consumption. MaxLinear provides an in-circuit EEPROM

programming utility through the USB interface using UART Control block 0x65. Refer to Table 5, “Control

Blocks,” on page 13. The EEPROM programming utility can be downloaded from the Exar website. These

values are uploaded from the EEPROM to the corresponding USB Standard Device Descriptor or Standard

Configuration Descriptor. For details of the USB Descriptors, refer to the USB 2.0 specifications.

TABLE 3:

ADDRESS CONTENTS

0Vendor ID (LSB)

1Vendor ID (MSB)

2Product ID (LSB)

3Product ID (MSB)

4Device Attributes

5Device Maximum Power

6Reserved

7Signature of 0x58 (’X’). If the signature is not correct, the contents of the EEPROM are ignored.

EEPROM CONTENTS

1.3.1.1 Vendor ID

The Vendor ID value replaces the idVendor field in the USB Standard Device Descriptor.

1.3.1.2 Product ID

The Product ID value replaces the idProduct field in the USB Standard Device Descriptor.

EEPROM

XR21V1410

REV. 1.4.1 1-CH FULL-SPEED USB UART

1.3.1.3 Device Attributes

The Device Attributes value replaces the bmAttributes field in the USB Standard Configuration Descriptor. The

default setting in the XR21V1410 device is 0xA0. The bit field definitions are:

Bit 7 is reserved - set to ’1’

Bit 6 is Self-powered mode - set to ’0’ for bus-powered, set to ’1’ for self-powered

Bit 5 is Remote Wakeup support - set to ’0’ for no support, set to ’1’ for remote wakeup support

Bit 4:0 are reserved - set to ’0’

1.3.1.4 Device Maximum Power

The Device Maximum Power value replaces the bMaxPower field in the USB Standard Configuration

Descriptor. The value specified is in units of 2 mA. For example, the value 0x2F is decimal 47 or 94 mA. Note

that the default bMaxPower of the XR21V1410 device is 94 mA.

1.4 UART Manager

The UART Manager enables/disables the UART including the TX and RX FIFOs. The UART Manager is

located in a separate register block from the UART registers.

1.5 UART

The UART can be configured via USB control transfers from the USB host. The UART transmitter and receiver

sections are described seperately in the following sections. At power-up, the XR21V1410 will default to 9600

bps, 8 data bits, no parity bit, 1 stop bit, and no flow control. If a standard CDC driver accesses the

XR21V1410, defaults will change. See ”Section 1.2, USB Device Driver” on page 5.

1.5.1 Transmitter

The transmitter consists of a 128-byte TX FIFO and a Transmit Shift Register (TSR). Once a bulk-out packet

has been received and the CRC has been validated, the data bytes in that packet are written into the TX FIFO

of the specified UART channel. Data from the TX FIFO is transferred to the TSR when the TSR is idle or has

completed sending the previous data byte. The TSR shifts the data out onto the TX output pin at the data rate

defined by the CLOCK_DIVISOR and TX_CLOCK_MASK registers. The transmitter sends the start bit

followed by the data bits (starting with the LSB), inserts the proper parity-bit if enabled, and adds the stop-

bit(s). The transmitter can be configured for 7 or 8 data bits with or without parity or 9 data bits without parity.

If 9 bit data is selected without wide mode, the 9th bit will always be ’0’.

1.5.1.1 Wide Mode Transmit

When both 9 bit data and wide mode are enabled, two bytes of data must be written. The first byte that is

loaded into the TX FIFO are the first 8 bits (data bits 7-0) of the 9-bit data. Bit-0 of the second byte that is

loaded into the TX FIFO is bit-8 of the 9-bit data. The data that is transmitted on the TX pin is as follows: start

bit, 9-bit data, stop bit. Use the WIDE_MODE register to enable wide mode.

1.5.2 Receiver

The receiver consists of a 384-byte RX FIFO and a Receive Shift Register (RSR). Data that is received in the

RSR via the RX pin is transferred into the RX FIFO. Data from the RX FIFO is sent to the USB host in

response to a bulk-in request. Depending on the mode, error / status information for that data character may

or may not be stored in the RX FIFO with the data.

1.5.2.1 Normal receive operation with 7 or 8-bit data

Data that is received is stored in the RX FIFO. Any parity, framing or overrun error or break status information

related to the data is discarded. Receive data format is shown in Figure 3.

1.5.2.2 Normal receive operation with 9-bit data

The first 8 bits of data received is stored in the RX FIFO. The 9th bit as well as any parity, framing or overrun

error or break status information related to the data is discarded.

XR21V1410

1-CH FULL-SPEED USB UART REV. 1.4.1

FIGURE 3.

ST byte

7, 8, or 9 bit data

76543210 7 = ‘0’ in 7 bit mode

NORMAL OPERATION RECEIVE DATA FORMAT

1.5.2.3 Wide mode receive operation with 7 or 8-bit data

Two bytes of data are loaded into the RX FIFO for each byte of data received. The first byte is the received

data. The second byte consists of the error bits and break status. Wide mode receive data format is shown in

Figure 4.

1.5.2.4 Wide mode receive operation with 9-bit data

Two bytes of data are loaded into the RX FIFO for each byte of data received. The first byte is the first 8 bits of

the received data. The 9th bit received is stored in the bit 0 of the second byte. The parity bit is not received /

checked. The remainder of the 2nd byte consists of the framing and overrun error bits and break status.

FIGURE 4. WIDE MODE RECEIVE DATA FORMAT

1st byte

2nd byte

9 bit mode

7 6 5 4 3 2 1 0

x x x x O F B P

1st byte

B = Break

F = Framing Error

O = Overrun Error

2nd byte

7 or 8 bit mode

P = Parity Error (= ‘0’ if not enabled)

7 = ‘0’ in 7 bit mode

x = ‘0’

7 6 5 4 3 2 1 0

x x x x O F B 8B = Break

F = Framing Error

O = Overrun Error

x = ‘0’

Error flags are also available from the ERROR_STATUS register and the interrupt packet, however these flags

are historical flags indicating that an error has occurred since the previous request. Therefore, no conclusion

can be drawn as to which specific byte(s) may have contained an actual error in this manner.

1.5.3 Rx FIFO Low Latency

In normal operation all bulk-in transfers will be of maxPacketSize (64) bytes to improve throughput and to

minimize host processing. When there are 64 bytes of data in the RX FIFO, the XR21V1410 will acknowledge

a bulk-in request from the host and transfer the data packet. If there is less than 64 bytes in the RX FIFO, the

XR21V1410 may NAK the bulk-in request indicating that data is not ready to transfer at that time. However, if

there is less than 64 bytes in the RX FIFO and no data has been received for more than 3 character times, the

XR21V1410 will acknowledge the bulk-in request and transfer any data in the RX FIFO to the USB host.

In some cases, especially when the baud rate is low, this increases latency unacceptably. The XR21V1410

has a low latency register bit that will cause the XR21V1410 to immediately transfer any received data in the

XR21V1410

REV. 1.4.1 1-CH FULL-SPEED USB UART

RX FIFO to the USB host, i.e. it will not wait for 3 character times. The custom driver can automatically set the

RX_FIFO_LOW_LATENCY register bit to force the XR21V1410 to be in the low latency mode, or the user may

manually set this bit. With the CDC-ACM driver, the low latency mode is automatically set whenever the baud

rate is set to a value of less than 46921 bps using the CDC_ACM_IF_SET_LINE_CODING command.

1.5.4 GPIO

The UART has 6 GPIOs. By hardware default the GPIOs are configured as inputs but may be modified by a

custom driver. Additionally, there are several modes that can be enabled to add additional feature such as

auto RTS/CTS flow control, auto DTR/DSR flow control or auto RS-485 half duplex control. See Table 14.

1.5.5 Automatic RTS/CTS Hardware Flow Control

GPIO5 and GPIO4 of the UART channel can be enabled as the RTS# and CTS# signals for Auto RTS/CTS

flow control when GPIO_MODE[2:0] = ’001’ and FLOW_CONTROL[2:0] = ’001’. Automatic RTS flow control is

used to prevent data overrun errors in local RX FIFO by de-asserting the RTS signal to the remote UART.

When there is room in the RX FIFO, the RTS pin will be re-asserted. Automatic CTS flow control is used to

prevent data overrun to the remote RX FIFO. The CTS# input is monitored to suspend/restart the local

transmitter (see Figure 5):

FIGURE 5. AUTO RTS AND CTS FLOW CONTROL OPERATION

Transmitter

Auto CTS

Monitor

Receiver FIFO

Trigger Reached

Auto RTS

Trigger Level

Remote UAR T

UARTB

RTSA#

CTSB#

TXB

RXA

ON ON

OFF

ON ON

OFF

1) COM port opened, RX FIFO empty, RTSA# output is asserted

2) Signal propagated to CTSB# input

3) Data bytes enter TX FIFO, begin transmitting on TXB

4) Data propagates to Receiving device RXA

5) RX FIFO reaches threshold

6) RTSA# de-asserts

7) Signal propagates to CTSB# input

8) Transmission stops on TXB

9) USB Bulk-In empties RX FIFO below threshold, RTSA# is asserted

10) Signal propagated to CTSB# input

11) Data bytes resume transmitting on TXB

RTSA# CTSB#

TXBRXA

CTSA#

TXA

RTSB#

RXB

Receiver FIFO

Trigger Reached

Auto RTS

Trigger Level

Transmitter

Auto CTS

Monitor

Local UART

UARTA

1.5.6 Automatic DTR/DSR Hardware Flow Control

Auto DTR/DSR hardware flow control behaves the same as the Auto RTS/CTS hardware flow control

described above except that it uses the DTR# and DSR# signals. For Auto hardware flow control,

FLOW_CONTROL[2:0] = ’001’. GPIO3 and GPIO2 become DTR# and DSR#, respectively, when

GPIO_MODE[2:0] = ’010’.

XR21V1410

1-CH FULL-SPEED USB UART REV. 1.4.1

1.5.7 Automatic XON/XOFF Software Flow Control

When software flow control is enabled, the XR21V1410 compares the receive data characters with the

programmed Xon or Xoff characters. If the received character matches the programmed Xoff character, the

XR21V1410 will halt transmission as soon as the current character has completed transmission. Data

transmission is resumed when a received character matches the Xon character. Software flow control is

enabled when FLOW_CONTROL[2:0] = ’010’.

1.5.8 Auto RS-485 Half-Duplex Control

The Auto RS-485 Half-Duplex Control feature changes the behavior of the GPIO5/RTS#/RS485 pin when

enabled by the GPIO_MODE register bits 2-0. See ”Section 3.3.12, GPIO_MODE Register Description (Read/Write)”

on page 22. The FLOW_CONTROL register must also be set appropriately for use in multidrop applications.

See ”Section 3.3.6, FLOW_CONTROL Register Description (Read/Write)” on page 19. If enabled, the transmitter

automatically asserts the GPIO5/RTS#/RS485 output prior to sending the data. By default, it de-asserts

GPIO5/RTS#/RS485 following the last stop bit of the last character that has been transmitted, but the

RS485_DELAY register may be used to delay the deassertion. The polarity of the GPIO5/RTS#/RS485 signal

may also be modified using the GPIO_MODE register bit 3.

1.5.9 Multidrop Mode with address matching

The XR21V1410 device has two address matching modes which are also set by the flow control register using

modes 3 and 4. These modes are intended for a multi-drop network application. In these modes, the

XON_CHAR register holds a unicast address and the XOFF_CHAR holds a multicast address. A unicast

address is used by a transmitting master to broadcast an address to all attached slave devices that is intended

for only one slave device. A multicast address is used to broadcast an address intended for more than one

recipient device. Each attached slave device should have a unique unicast address value stored in the

XON_CHAR register, while multiple slaves may have the same multicast adderss stored in the XOFF_CHAR

value stored in either the XON_CHAR or XOFF_CHAR register.

1.5.9.1 Receiver

If an address match occurs in either flow control mode 3 or 4, the address byte will not be loaded into the RX

FIFO, but all subsequent data bytes will be loaded into the RX FIFO. The UART Receiver will automatically be

disabled when an address byte is received that does not match the values in the XON_CHAR or XOFF_CHAR

1.5.9.2 Transmitter

In flow control mode 3, the UART transmitter is always enabled, irrespective of the Rx address match. In flow

control mode 4, the UART transmitter will only be enabled if there is an Rx address match.

1.5.10 Programmable Turn-Around Delay

By default, the GPIO5/RTS#/RS485 pin will be de-asserted immediately after the stop bit of the last byte has

been shifted when auto RS-485 half-duplex control is enabled by the GPIO_MODE register. However, this

may not be ideal for systems where the signal needs to propagate over long cables. Therefore, the de-

assertion of GPIO5/RTS#/RS485 pin can be delayed from 1 to 15 bit times via the RS485_DELAY register to

allow for the data to reach distant UARTs.

1.5.11 Half-Duplex Mode

Half-duplex mode is enabled when FLOW_CONTROL[3] = 1. In this mode, the UART will ignore any data on

the RX input when the UART is transmitting data.

1.5.12 USB Suspend

All USB peripheral devices must support the USB suspend mode. Per USB standard, the XR21V1410 device

will begin to enter the Suspend state if it does not detect any activity (including Start of Frame or SOF packets)

on its USB data lines for 3 ms. The device must then reduce power consumption from VBUS power within the

next 7 ms to the allowed limit of 2.5 mA for the suspended state. Note that in this context, the "device" is all

circuitry (including the XR21V1410) that draws power from the host VBUS.

XR21V1410

REV. 1.4.1 1-CH FULL-SPEED USB UART

1.5.13 Remote Wakeup

When the XR21V1410 is suspended, the GPIO0/RI#/RWK# pin can be used to request that the host exit the

Suspend state. A high to low transition on this pin will cause the device to signal a remote wakeup request to

the host via a custom driver. Note that the standard CDC-ACM driver does not support this feature. In order

for the remote wakeup to work, several things must be properly configured. First, the GPIO0/RI#/RWK# pin

must be configured as an input. Additionally, the XR21V1410 device must have the remote wakeup feature

support indicated in the USB attributes - See “Section 1.3, I2C Interface” on page 6. Lastly, a custom software

driver must inform the USB host that the peripheral device supports the remote wake-up feature.

XR21V1410

1-CH FULL-SPEED USB UART REV. 1.4.1

2.0 USB CONTROL COMMANDS

The following table shows all of the USB Control Commands that are supported by the XR21V1410.

Commands included are standard USB commands, CDC-ACM commands and custom Exar commands.

TABLE 4: SUPPORTED USB CONTROL COMMANDS

NAME REQUEST

TYPE REQUEST VALUE INDEX LENGTH DESCRIPTION

DEV GET_STATUS 0x80 0 0 0 0 0 2 0 Device: remote wake-up +

self-powered

IF GET_STATUS 0x81 0 0 0 1-4,

129-

132

020

Interface: zero

EP GET_STATUS 0x82 0 0 0 0-4,

129-

136

020

Endpoint: halted

DEV CLEAR_FEATURE 0x00 1 1 0 0 0 0 0 Device remote wake-up

EP CLEAR_FEATURE 0x02 1 0 0 0-4,

129-

136

000

Endpoint halt

DEV SET_FEATURE 0x00 3 1 00 0 0 0 0 Device remote wake-up

DEV SET_FEATURE 0x00 3 2 0 0 test 0 0 Test mode

EP SET_FEATURE 0x02 3 0 0 0-4,

129-

136

000

Endpoint halt

SET_ADDRESS 0x00 5addr 0 0 0 0 0

GET_DESCRIPTOR 0x80 6 0 1 0 0 len

LSB

len

MSB Device descriptor

GET_DESCRIPTOR 0x80 6 0 2 0 0 len

LSB

len

MSB Configuration descriptor

GET_CONFIGURATION 0x80 8 0 0 0 0 1 0

SET_CONFIGURATION 0x00 9 n 0 0 0 0 0

GET_INTERFACE 0x81 10 0 0 0-7 010

CDC_ACM_IF

SET_LINE_CODING

0x21 32 0 0 0, 2,

4, 6

070Set the UART baud rate,

parity, stop bits, etc.

CDC_ACM_IF

GET_LINE_CODING

0xA1 33 0 0 0, 2,

4, 6

070Get the UART baud rate,

parity, stop bits, etc.

CDC_ACM_IF SET_-

CONTROL_LINE_

STATE

0x21 34 val 00, 2,

4, 6

000

Set UART control lines

XR21V1410

REV. 1.4.1 1-CH FULL-SPEED USB UART

2.1 UART Block Numbers

The table below lists the block numbers for accessing each of the UART channels and the UART Manager.

TABLE 5: CONTROL BLOCKS

BLOCK NAME BLOCK NUMBER DESCRIPTION

UART 0The configuration and control registers for the UART.

UART Manager 4The control registers for the UART Manager. The UART Manager

enables/disables the TX and RX FIFOs for each UART.

I2C EEPROM 0x65 Accesses external EEPROM via I2C interface.

UART Custom 0x66 Custom UART control registers. Enables / disables for wide mode, low

latency mode and custom interrupt packet.

CDC_ACM_IF

SEND_BREAK

0x21 35 val

LSB

val

MSB

0, 2,

4, 6

000 Send a break for the

specified duration

XR_SET_REG 0x40 0val 0regis-

ter

block 0 0 Exar custom command: set

one 8-bit register

val: 8-bit register value

Tabl e 7

block number: see Table 5

XR_GETN_REG 0xC0 1 0 0 regis-

ter

block count

LSB

count

MSB

Exar custom register: get

count 8-bit registers

Tabl e 7

block number: see Table 5

TABLE 4: SUPPORTED USB CONTROL COMMANDS

NAME REQUEST

TYPE REQUEST VALUE INDEX LENGTH DESCRIPTION

XR21V1410

1-CH FULL-SPEED USB UART REV. 1.4.1

3.0 REGISTER SET DESCRIPTION

The internal register set of the XR21V1410 consists of 3 different blocks of registers: the UART Manager,

UART registers and UART miscellaneous registers. The UART Manager controls the TX and RX enables and

FIFOs of all UART channels. The UART registers configure and control the remaining UART channel

functionality with the exception of low latency mode, wide mode and custom interrupt packet enables in the

UART custom register block.

Registers are accessed only via the USB interface by the XR_SET_REG and XR_GET_REG commands listed

in Table 4. The register address offsets are given in Table 6, Ta b le 7 and Tab l e 15, and the register blocks are

given in Ta ble 5.

3.1 UART Manager Registers

TABLE 6: UART MANAGER REGISTERS

ADDRESS REGISTER NAME BIT-7 BIT-6 BIT-5 BIT-4 BIT-3 BIT-2 BIT-1 BIT-0

0X10 FIFO_ENABLE 000000RX TX

0X18 RX_FIFO_RESET Bit-7 Bit-6 Bit-5 Bit-4 Bit-3 Bit-2 Bit-1 Bit-0

0x1C TX_FIFO_RESET Bit-7 Bit-6 Bit-5 Bit-4 Bit-3 Bit-2 Bit-1 Bit-0

3.1.1 FIFO_ENABLE Registers

Enables the RX FIFO and TX FIFOs. For proper functionality, the UART TX and RX must be enabled in the

following order:

FIFO_ENABLE = 0x1 // Enable TX FIFO

UART_ENABLE = 0x3 // Enable TX and RX

FIFO_ENABLE = 0x3 // Enable RX FIFO

3.1.2 RX_FIFO_RESET and TX_FIFO_RESET Registers

Writing a non-zero value to these registers resets the FIFOs.

XR21V1410

REV. 1.4.1 1-CH FULL-SPEED USB UART

3.2 UART Register Map

TABLE 7: UART REGISTERS

ADDRESS REGISTER NAME BIT-7 BIT-6 BIT-5 BIT-4 BIT-3 BIT-2 BIT-1 BIT-0

0X00 Reserved 00000000

0X01 Reserved 00000000

0X02 Reserved 00000000

0X03 UART_ENABLE 000000RX TX

0X04 CLOCK_DIVISOR0 Bit-7 Bit-6 Bit-5 Bit-4 Bit-3 Bit-2 Bit-1 Bit-0

0x05 CLOCK_DIVISOR1 Bit-15 Bit-14 Bit-13 Bit-12 Bit-11 Bit-10 Bit-9 Bit-8

0x06 CLOCK_DIVISOR2 00000Bit-18 Bit-17 Bit-16

0x07 TX_CLOCK_MASK0 Bit-7 Bit-6 Bit-5 Bit-4 Bit-3 Bit-2 Bit-1 Bit-0

0x08 TX_CLOCK_MASK1 Bit-15 Bit-14 Bit-13 Bit-12 Bit-11 Bit-10 Bit-9 Bit-8

0x09 RX_CLOCK_MASK0 Bit-7 Bit-6 Bit-5 Bit-4 Bit-3 Bit-2 Bit-1 Bit-0

0x0A RX_CLOCK_MASK1 Bit-15 Bit-14 Bit-13 Bit-12 Bit-11 Bit-10 Bit-9 Bit-8

0x0B CHARACTER_FORMAT Stop Parity Data Bits

0x0C FLOW_CONTROL 0000Half-

Duplex Flow Control Mode Select

0x0D Reserved 00000000

0x0E Reserved 00000000

0x0F Reserved 00000000

0x10 XON_CHAR Bit-7 Bit-6 Bit-5 Bit-4 Bit-3 Bit-2 Bit-1 Bit-0

0x11 XOFF_CHAR Bit-7 Bit-6 Bit-5 Bit-4 Bit-3 Bit-2 Bit-1 Bit-0

0x12 LOOPBACK_CTL 00000En 0 0

0x13 ERROR_STATUS Break

Status

Overrun

Error

Parity

Error

Framing

Error

Break

Error 000

0x14 TX_BREAK Bit-7 Bit-6 Bit-5 Bit-4 Bit-3 Bit-2 Bit-1 Bit-0

0x15 RS485_DELAY 0000 Delay

0x16 Reserved 00000000

0x17 Reserved 00000000

0x18 Reserved 00000000

0x19 Reserved 00000000

0x1A GPIO_MODE 0000RS485

Polarity Mode Select

0x1B GPIO_DIRECTION 0 0 GPIO5 GPIO4 GPIO3 GPIO2 GPIO1 GPIO0

0x1C GPIO_INT_MASK 0 0 GPIO5 GPIO4 GPIO3 GPIO2 GPIO1 GPIO0

0x1D GPIO_SET 0 0 GPIO5 GPIO4 GPIO3 GPIO2 GPIO1 GPIO0

0x1E GPIO_CLEAR 0 0 GPIO5 GPIO4 GPIO3 GPIO2 GPIO1 GPIO0

0x1F GPIO_STATUS 0 0 GPIO5 GPIO4 GPIO3 GPIO2 GPIO1 GPIO0

XR21V1410

1-CH FULL-SPEED USB UART REV. 1.4.1

3.3 UART Register Descriptions

All register bits default to a value of ’0’ unless otherwise noted.

3.3.1 UART_ENABLE Register Description (Read/Write)

This register enables the UART TX and RX. For proper functionality, the UART TX and RX must be enabled in

the following order:

FIFO_ENABLE = 0x1 // Enable TX FIFO

UART_ENABLE = 0x3 // Enable TX and RX of that channel

FIFO_ENABLE = 0x3 // Enable RX FIFO

UART_ENABLE[0]: Enable UART TX

Logic 0 = UART TX disabled.

Logic 1 = UART TX enabled.

UART_ENABLE[1]: Enable UART RX

Logic 0 = UART RX disabled.

Logic 1 = UART RX enabled.

UART_ENABLE[7:2]: Reserved

These bits are reserved and should remain ’0’.

3.3.2 CLOCK_DIVISOR0, CLOCK_DIVISOR1, CLOCK_DIVISOR2 Register Description (Read/Write)

These registers are used for programming the baud rate. The XR21V1410 uses a 19-bit divisor and 16-bit

mask register. Using the internal 48MHz oscillator, the 19-bit divisor is calculated as follows:

CLOCK_DIVISOR = Trunc ( 48000000 / Baud Rate )

For example, if the the baud rate is 115200bps, then

CLOCK_DIVISOR = Trunc ( 48000000 / 115200 ) = Trunc (416.66667) = 416

CLOCK_DIVISOR0[7:0]: Baud rate clock divisor bits [7:0]

CLOCK_DIVISOR1[7:0]: Baud rate clock divisor bits [15:8]

CLOCK_DIVISOR2[2:0]: Baud rate clock divisor bits [18:16]

CLOCK_DIVISOR2[7:3]: Reserved

These bits are reserved and should remain ’0’.

3.3.3 TX_CLOCK_MASK0, TX_CLOCK_MASK1 Register Description (Read/Write)

A look-up table is used for the value of the 16-bit TX Clock mask registers. The index of the look-up table is

calculated as follows:

index = Trunc ( ( ( 48000000 / Baud Rate ) - CLOCK_DIVISOR ) * 32)

For example, if the baud rate is 115200bps, then the index will be:

index = Trunc ( ( ( 48000000 / 115200 ) - 416 ) * 32) = Trunc (21.3333) = 21

The values for some baud rates to program the TX_CLOCK_MASK registers are listed in Table 8. For baud

rates that are not listed, use the index to select TX_CLOCK_MASK register values from Table 9.

3.3.4 RX_CLOCK_MASK0, RX_CLOCK_MASK1 Register Description (Read/Write)

The values for some example baud rates to program the RX_CLOCK_MASK registers are listed in Ta b l e 8. For

baud rates that are not listed, use the same index calculated for the TX_CLOCK_MASK register to select

RX_CLOCK_MASK register values from Ta b l e 9.

TABLE 8: CLOCK DIVISOR AND CLOCK MASK VALUES FOR COMMON BAUD RATES

BAUD RATE (BPS) CLOCK DIVISOR (DECIMAL)TX CLOCK MASK (HEX)RX CLOCK MASK (HEX)

1200 40000 0x0000 0x0000

2400 20000 0x0000 0x0000

4800 10000 0x0000 0x0000

9600 5000 0x0000 0x0000

19200 2500 0x0000 0x0000

38400 1250 0x0000 0x0000

57600 833 0x0912 0x0924

115200 416 0x0B6D 0x0B6A

230400 208 0x0912 0x0924

460800 104 0x0208 0x0040

500000 96 0x0000 0x0000

576000 83 0x0912 0x0924

921600 52 0x0040 0x0000

1000000 48 0x0000 0x0000

1152000 41 0x0B6D 0x0DB6

1500000 32 0x0000 0x0000

2000000 24 0x0000 0x0000

2500000 19 0x0104 0x0108

3000000 16 0x0000 0x0000

3125000 15 0x0492 0x0492

3500000 13 0x076D 0x0BB6

4000000 12 0x0000 0x0000

4250000 11 0x0122 0x0224

6250000 70x0B6D 0x0DB6

8000000 60x0000 0x0000

12000000 40x0000 0x0000

XR21V1410

REV. 1.4.1 1-CH FULL-SPEED USB UART

For baud rates that are not listed in the table above, use the index value calcuated using the formula in “Section

3.3.3, TX_CLOCK_MASK0, TX_CLOCK_MASK1 Register Description (Read/Write)” on page 16 to determine which TX

Clock and RX Clock Mask register values to use from Tab l e 9. For the the RX Clock Mask register, there are 2

values listed and would depend on whether the Clock Divisor is even or odd. For even Clock Divisors, use the

value from the first column. For odd Clock Divisors, use the value from the last column.

XR21V1410

1-CH FULL-SPEED USB UART REV. 1.4.1

TABLE 9:

INDEX

(DECIMAL)TX CLOCK MASK (HEX)RX CLOCK MASK (HEX) -

EVEN CLOCK DIVISOR

RX CLOCK MASK (HEX) -

ODD CLOCK DIVISOR

00x0000 0x0000 0x0000

10x0000 0x0000 0x0000

20x0100 0x0000 0x0100

30x0020 0x0400 0x0020

40x0010 0x0100 0x0010

50x0208 0x0040 0x0208

60x0104 0x0820 0x0108

70x0844 0x0210 0x0884

80x0444 0x0110 0x0444

90x0122 0x0888 0x0224

10 0x0912 0x0448 0x0924

11 0x0492 0x0248 0x0492

12 0x0252 0x0928 0x0292

13 0x094A 0x04A4 0x0A52

14 0x052A 0x0AA4 0x054A

15 0x0AAA 0x0954 0x04AA

16 0x0AAA 0x0554 0x0AAA

17 0x0555 0x0AD4 0x05AA

18 0x0B55 0x0AB4 0x055A

19 0x06B5 0x05AC 0x0B56

20 0x05B5 0x0D6C 0x06D6

21 0x0B6D 0x0B6A 0x0DB6

22 0x076D 0x06DA 0x0BB6

23 0x0EDD 0x0DDA 0x076E

24 0x0DDD 0x0BBA 0x0EEE

25 0x07BB 0x0F7A 0x0DDE

26 0x0F7B 0x0EF6 0x07DE

27 0x0DF7 0x0BF6 0x0F7E

28 0x07F7 0x0FEE 0x0EFE

29 0x0FDF 0x0FBE 0x07FE

30 0x0F7F 0x0EFE 0x0FFE

31 0x0FFF 0x0FFE 0x0FFD

TTX AND RX CLOCK MASK VALUES

XR21V1410

REV. 1.4.1 1-CH FULL-SPEED USB UART

3.3.5 CHARACTER_FORMAT Register Description (Read/Write)

This register controls the character format such as the word length (7, 8 or 9), parity (odd, even, forced ’0’, or

forced ’1’) and number of stop bits (1 or 2).

CHARACTER_FORMAT[3:0]: Data Bits.

TABLE 10: DATA BITS

DATA BITS CHARACTER_FORMAT[3:0]

70111

81000

91001

All other values for CHARACTER_FORMAT[3:0] are reserved.

CHARACTER_FORMAT[6:4]: Parity Mode Select

These bits select the parity mode. If 9-bit data mode has been selected, then writing to these bits will not have

any effect. In other words, there will not be an additional parity bit.

TABLE 11: PARITY SELECTION

BIT-6 BIT-5 BIT-4 PARITY SELECTION

0 0 0 No parity

0 0 1 Odd parity

0 1 0 Even parity

0 1 1 Force parity to mark, “1”

1 0 0 Force parity to space, “0”

CHARACTER_FORMAT[7]: Stop Bit select

This register selects the number of stop bits to add to the transmitted character and how many stop bits to

check for in the received character.

TABLE 12: STOP BIT SELECTION

BIT-7 NUMBER OF STOP BITS

01 stop bit

22 stop bits

3.3.6 FLOW_CONTROL Register Description (Read/Write)

These registers select the flow control mode. These registers should only be written to when the UART is

disabled. Writing to the FLOW_CONTROL register when the UART is enabled will result in undefined

behavior. Note that the FLOW_CONTROL register settings are used in conjunction with the GPIO_MODE

XR21V1410

1-CH FULL-SPEED USB UART REV. 1.4.1

FLOW_CONTROL[2:0]: Flow control mode select

TABLE 13: FLOW CONTROL MODE SELECTION

MODE BIT-2 BIT-1 BIT-0 MODE DESCRIPTION

0 0 0 0 No flow control, no address matching.

1 0 0 1 HW flow control enabled. Auto RTS/CTS or DTR/DSR must be selected by

GPIO_MODE.

2 0 1 0 SW flow control enabled

3 0 1 1 Multidrop mode - RX only after address match, TX independent. (Typically

used with GPIO_MODE 3)

4 1 0 0 Multidrop mode - RX / TX only after address match. (Typically used with GPI-

O_MODE 4)

FLOW_CONTROL[3]: Half-Duplex Mode

Logic 0 = Normal (full-duplex) mode. The UART can transmit and receive data at the same time.

Logic 1 = Half-duplex Mode. In half-duplex mode, any data on the RX pin is ignored when the UART is

transmitting data.

FLOW_CONTROL[7:4]: Reserved

These bits are reserved and should remain ’0’.

3.3.7 XON_CHAR, XOFF_CHAR Register Descriptions (Read/Write)

The XON_CHAR and XOFF_CHAR registers store the XON and XOFF characters, respectively, that are used

in the Automatic Software Flow control. If the XR21V1410 is configured in multidrop mode, the XON_CHAR

and XOFF_CHAR registers are instead used for address matching.

XON_CHAR[7:0]: XON Character

In Automatic Software Flow control mode, the UART will resume data transmission when the XON character

has been received.

For behavior in the Address Match mode, see “Section 1.5.9, Multidrop Mode with address matching” on page 10.

XOFF_CHAR[7:0]: XOFF Character

In Automatic Software Flow control mode, the UART will suspend data transmission when the XOFF character

has been received.

For behavior in the Address Match mode, see “Section 1.5.9, Multidrop Mode with address matching” on page 10.

3.3.8 LOOPBACK_CTL Register Descriptions (Read/Write)

LOOPBACK_CTL[1:0]: Reserved

These bits are reserved and should remain ’0’.

LOOPBACK_CTL[2]: Enable

Logic 0 = Internal UART (TX to RX) loopback is disabled.

Logic 1 = Internal UART (TX to RX) loopback is enabled.

LOOPBACK_CTL[7:3]: Reserved

These bits are reserved and should remain ’0’.

XR21V1410

REV. 1.4.1 1-CH FULL-SPEED USB UART

3.3.9 ERROR_STATUS Register Description - Read-only

This register reports any errors that may have occurred on the line such as framing, parity and overrun as well

as break status.

ERROR_STATUS[2:0]: Reserved

These bits are reserved. Any values read from these bits should be ignored.

ERROR_STATUS[3]: Break status

Logic 0 = No break condition

Logic 1 = A break condition has been detected (clears after read).

ERROR_STATUS[4]: Framing Error

Logic 0 = No framing error

Logic 1 = A framing error has been detected (clears after read). A framing error occurs when a stop bit is not

present when it is expected.

ERROR_STATUS[5]: Parity Error

Logic 0 = No parity error

Logic 1 = A parity error has been detected (clears after read).

ERROR_STATUS[6]: Overrun Error

Logic 0 = No overrun error

Logic 1 = An overrun error has been detected (clears after read). An overrun error occurs when the RX FIFO

is full and another byte of data is received.

ERROR_STATUS[7]: Break Status

Logic 0 = Break condition is no longer present.

Logic 1 = Break condition is currently being detected.

3.3.10 TX_BREAK Register Description (Read/Write)

Writing a non-zero value to this register causes a break condition to be generated continuously until the

break condition is generated.

3.3.11 RS485_DELAY Register Description (Read/Write)

RS485_DELAY[3:0]: Turn-around delay

This is the number of bit times the XR21V1410 waits before de-asserting the GPIO5/RTS#/RS485 pin when it

is configured for automatic RS-485 half-duplex control.

RS485_DELAY[7:4]: Reserved

These bits are reserved and should be ’0’.

XR21V1410

1-CH FULL-SPEED USB UART REV. 1.4.1

3.3.12 GPIO_MODE Register Description (Read/Write)

GPIO_MODE[2:0]: GPIO Mode Select

There are 4 modes of operation for the GPIOs. The descriptions can be found in “Section 1.5, UART” on page 7.

TABLE 14: GPIO MODES

[2:0] GPIO0 GPIO1 GPIO2 GPIO3 GPIO4 GPIO5 MODE DESCRIPTION

000 GPIO0 GPIO1 GPIO2 GPIO3 GPIO4 GPIO5 GPIO Mode, All GPIO pins available as GPIO

001 GPIO0 GPIO1 GPIO2 GPIO3 CTS# RTS# GPIO4 and GPIO5 used for Auto RTS/CTS HW

Flow Control

010 GPIO0 GPIO1 DSR# DTR# GPIO4 GPIO5 GPIO2 and GPIO3 used for Auto DTR/DSR HW

Flow Control

011 GPIO0 GPIO1 GPIO2 GPIO3 GPIO4 RS485 GPIO5 used for auto RS-485 half-duplex control

100 GPIO0 GPIO1 GPIO2 GPIO3 GPIO4 RS485 GPIO5 used for auto RS-485 half-duplex control

after address match (See FLOW_CONTROL

mode 4).

GPIO_MODE[3]: RS485 Polarity

Logic 0 = GPIO5/RTS#/RS485 Low for TX

Logic 1 = GPIO5/RTS#/RS485 High for TX

GPIO_MODE[7:4]: Reserved

These register bits are reserved. When writing to these bits, the value should be ’0’. When reading from these

bits, they are undefined and should be ignored.

3.3.13 GPIO_DIRECTION Register Description (Read/Write)

This register controls the direction of pins configured as GPIO. (Pins configured for UART functions via the

GPIO_MODE register, e.g. RTS# are not controlled or reported in the GPIO_DIRECTION register.)

GPIO_DIRECTION[5:0]: GPIOx Direction

Logic 0 = GPIOx is an input.

Logic 1 = GPIOx is an output.

GPIO_DIRECTION[7:6]: Reserved

These register bits are reserved and should be ’0’.

3.3.14 GPIO_INT_MASK Register Description (Read/Write)

Enables / disables generation of a USB interrupt packet at the change of state of GPIO pins when they are

configured as inputs.

GPIO_INT_MASK[5:0]: GPIOx Interrupt Mask

Logic 0 = A change on this input does not cause the device to generate an interrupt packet.

Logic 1 = A change on this input causes the device to generate an interrupt packet.

GPIO_INT_MASK[7:6]: Reserved

These register bits are reserved and should be ’0’.

BITS

XR21V1410

REV. 1.4.1 1-CH FULL-SPEED USB UART

3.3.15 GPIO_SET Register Description (Read/Write)

Writing a ’1’ to the corresponding GPIO bit (5:0) of this register drives the GPIO output high. Writing a ’0’ to a

bit has no effect. Bits 7-6 are unused and should be ’0’.

3.3.16 GPIO_CLEAR Register Description (Read/Write)

Writing a ’1’ to the corresponding GPIO bit (5:0) of this register drives the GPIO output low. Writing a ’0’ to a bit

has no effect. Bits 7-6 are unused and should be ’0’.

3.3.17 GPIO_STATUS Register Description (Read-Only)

This register reports the current state of the GPIO pin.

3.4 UART Custom Registers

TABLE 15: UART CUSTOM REGISTERS

ADDRESS REGISTER NAME BIT-7 BIT-6 BIT-5 BIT-4 BIT-3 BIT-2 BIT-1 BIT-0

0X03 CUSTOM 000000MaxPkt-

Size

WIDE_

0x04 LOW_LATENCY 0000000EN

0x06 CUSTOM_INT_PACKET 0GPIO5 GPIO4 GPIO3 GPIO0 0GPIO2 GPIO1

3.4.1 CUSTOM Register Description (Read/Write)

This register controls the bMaxPacketSize and enables the Wide mode functionality for the UART.

CUSTOM[0]: Enable wide mode

Logic 0 = Normal (7, 8 or 9 bit data) mode

Logic 1 = Wide mode - See “Section 1.5.1.1, Wide Mode Transmit” on page 7, “Section 1.5.2.3, Wide mode receive

operation with 7 or 8-bit data” on page 8 and “Section 1.5.2.4, Wide mode receive operation with 9-bit data” on page 8.

CUSTOM[1]: Max Packet Size

Logic 0 = bMaxPacketSize = 64 bytes

Logic 1 = bMaxPacketSize = 63 bytes (this bit is automatically set to ’1’ if the XR21V1410 receives a

CDC_ACM USB command)

CUSTOM[7:2]: Reserved

These bits are reserved and should remain ’0’

3.4.2 LOW_LATENCY Register Description (Read/Write)

This register is automatically set to logic ’1’ for baud rates below 46921 bps, and can be manually set for baud

rates of 46921 bps and higher. This register enables the Low latency feature of the UART. Write to this

LOW_LATENCY[0]: Enable Low Latency mode

Logic 0 = Receive data is not forwarded from the Rx FIFO until bMaxPacketSize (64 bytes) or timeout (3

characters) has occurred.

Logic 1 = All data in the RX FIFO is provided to the USB host at the next BULK IN request irrespective of the

number of bytes in the FIFO.

LOW_LATENCY[7:1]: Reserved

These bits are reserved and should remain ’0’.

XR21V1410

1-CH FULL-SPEED USB UART REV. 1.4.1

3.4.3 CUSTOM_INT_PACKET (Read/Write)

This register is used to enable / disable GPIO status in the high data byte of the custom interrupt packet. See

Table 16, “Interrupt Packet Format,” on page 25 and Ta b l e 18, “Data Field of Customized Interrupt Packet - Exar Vendor

Specific,” on page 26.

CUSTOM_INT_PACKET[0]: GPIO1

Logic 0 = Disable GPIO1 status in custom interrupt packet.

Logic 1 = Enable GPIO1 status in custom interrupt packet.

CUSTOM_INT_PACKET[1]: GPIO2

Logic 0 = Disable GPIO2 status in custom interrupt packet.

Logic 1 = Enable GPIO2 status in custom interrupt packet.

CUSTOM_INT_PACKET[2]: Reserved

This bit is reserved and should remain ’0’.

CUSTOM_INT_PACKET[3]: GPIO0

Logic 0 = Disable GPIO0 status in custom interrupt packet.

Logic 1 = Enable GPIO0 status in custom interrupt packet.

CUSTOM_INT_PACKET[4]: GPIO3

Logic 0 = Disable GPIO3 status in custom interrupt packet.

Logic 1 = Enable GPIO3 status in custom interrupt packet.

CUSTOM_INT_PACKET[5]: GPIO4

Logic 0 = Disable GPIO4 status in custom interrupt packet.

Logic 1 = Enable GPIO4 status in custom interrupt packet.

CUSTOM_INT_PACKET[6]: GPIO5

Logic 0 = Disable GPIO5 status in custom interrupt packet.

Logic 1 = Enable GPIO5 status in custom interrupt packet.

CUSTOM_INT_PACKET[7]: Reserved

This bit is reserved and should remain ’0’.

XR21V1410

REV. 1.4.1 1-CH FULL-SPEED USB UART

TABLE 16: INTERRUPT PACKET FORMAT

OFFSET FIELD SIZE

(BYTES)VALUE DESCRIPTION

0bmRequestType 18’b10100001 D7 = Device-to-host direction

D6:5 = Class Type

D4-0: = Interface Recipient

1bNotification 18’h20 Defined encoding for SERIAL_STATE

2wValue 216’h0000

4wIndex 216’h0000 D15-8 = Reserved (0)

D7-0 = Interface number, 8’h00 for the CDC 

Command Interface

6wLength 216’h0002 2 bytes of transferred data

8Data 2Standard

int_status

(See Ta b le 17 or

Table 18)

D15-7 = Reserved (0)

D6 = bOverRun

D5 = bParity

D4 = bFraming

D3 = bRingSignal (RI)

D2 = bBreak

D1 = bTxCarrier (DSR)

D0 = bRxCarrier (CD)

TABLE 17:

BIT(S) FIELD DESCRIPTION

D15..D7 Reserved (0)

D6 bOverRun Received data has been discarded due to overrun in the device.

D5 bParity A parity error has occurred.

D4 bFraming A framing error has occurred.

D3 bRingSignal State of ring signal detection of the device.

D2 bBreak State of break detection mechanism of the device.

D1 bTxCarrier State of transmission carrier. This signal corresponds to V.24 signal 106 and

RS-232 signal DSR.

D0 bRxCarrier State of receiver carrier detection mechanism of device. This signal 

corresponds to V.24 signal 109 and RS-232 signal DCD.

DATA FIELD OF STANDARD INTERRUPT PACKET

If the Exar vendor specific packet mapping is enabled then the data field also includes status for all of the

UART / GPIO pins as follows:

XR21V1410

1-CH FULL-SPEED USB UART REV. 1.4.1

TABLE 18:

BIT(S) FIELD DESCRIPTION

15 D15 Reserved (0)

14 D14 bGPIO5 (RTS)

13 D13 bGPIO4 (CTS)

12 D12 bGPIO3 (DTR)

11 D11 bGPIO0 (RI)

10 D10 Reserved (0)

9D9 bGPIO2 (DSR)

8D8 bGPIO1 (CD)

7D7 Reserved (0)

6D6 bOverRun

5D5 bParity

4D4 bFraming

3D3 bRingSignal (RI)

2D2 bBreak

1D1 bTxCarrier (DSR)

0D0 bRxCarrier (CD)

DATA FIELD OF CUSTOMIZED INTERRUPT PACKET - EXAR VENDOR SPECIFIC

XR21V1410

REV. 1.4.1 1-CH FULL-SPEED USB UART

4.0 ELECTRICAL CHARACTERISTICS

TABLE 19: ABSOLUTE MAXIMUM RATINGS

PARAMETER RATING UNIT

Vcc Supply Voltage + 4.0 V

Input Voltage (all pins except USBD+ and USBD-) - 0.3 to + 6.0 V

Input Voltage (USBD+ and USBD-) - 0.3 to + 5.75 V

Junction Temperature 125 OC

DC ELECTRICAL CHARACTERISTICS - POWER CONSUMPTION

UNLESS OTHERWISE NOTED: T O TO +85O IS 2.97 TO 3.63V

SYMBOL PARAMETER

LIMITS

MIN TYP MAX

UNITS CONDITIONS

ICC Power Supply Current 16 20 mA

ISusp Suspend mode Current 1.5 1.65 mA

DC ELECTRICAL CHARACTERISTICS - UART, LOWPOWER & GPIO PINS

UNLESS OTHERWISE NOTED: T O TO +85O IS 2.97 TO 3.63V

SYMBOL PARAMETER

LIMITS

MIN MAX

UNITS CONDITIONS

VIL Input Low Voltage -0.3 0.8 V

VIH Input High Voltage 2.0 5.5 V

VOL Output Low Voltage 0.3 V IOL = 4mA

VOH Output High Voltage 2.2 V IOH = -4mA

IIL Input Low Leakage Current ±10 uA

IIH Input High Leakage Current ±10 uA

CIN Input Pin Capacitance 5pF

A = -40 C, VCC

3.3V

A = -40 C, VCC

3.3V

DC ELECTRICAL CHARACTERISTICS - USB I/O PINS

UNLESS OTHERWISE NOTED: T O TO +85O IS 2.97 TO 3.63V

SYMBOL PARAMETER

LIMITS

MIN MAX

UNITS CONDITIONS

VIL Input Low Voltage -0.3 0.8 V

VIH Input High Voltage 2.0 5.5 V

VOL Output Low Voltage 00.3 VExternal 15 KOhm to

GND on USBD- pin

VOH Output High Voltage 2.8 3.6 VExternal 15 KOhm to

GND on USBD- pin

VDrvZ Driver Output Impedance 28 44 Ohms

IOSC Open short current Current 38.5 mA 1.5 V on USBD+ and

USBD-

XR21V1410

1-CH FULL-SPEED USB UART REV. 1.4.1

A = -40 C, VCC

3.3V

XR21V1410

REV. 1.4.1 1-CH FULL-SPEED USB UART

MECHANICAL DIMENSIONS (16 PIN QFN - 3 X 3 X 0.9 mm)

Revision: A

Drawing No.: POD-

TOP VIEW

TERMINAL DETAILS

SIDE VIEW

BOTTOM VIEW

16X L

16X b

00000138

NOTE: QFN16 θJA = 36.4 ᵒC/W, θJC = 17.8 ᵒC/W. All values are typical.

RECOMMENDED LAND PATTERN AND STENCIL

Revision: A

Drawing No.: POD-

TYPICAL RECOMMENDED STENCIL

TYPICAL RECOMMENDED LAND PATTERN

00000138

XR21V1410

1-CH FULL-SPEED USB UART REV. 1.4.1

REVISION HISTORY

DATE REVISION DESCRIPTION

June 2009 1.0.0 Released Datasheet

September 2010 1.1.0 Clarified pin functionality, wide mode and low latency mode including registers /

blocks, clarified FLOW_CONTROL and GPIO_MODE register functionality.

April 2011 1.2.0 Updated ordering information, SDA/SCL pin types, modified GPIO0 pin name and

added LOOPBACK_CTL register and description.

April 2012 1.3.0 Updated LOWPOWER pin description, bMaxPacketSize and DC electrical character-

isitics. See PCN12-0305-01 for more details.

July 2013 1.3.1 Updated package drawing QFN16

January 2014 1.4.0 Added Windows driver versions, added absolute maximum tables, added ESD pro-

tection ratings, added QFN package center pad to pin descriptions, minor clarifica-

tions including requirement for even Product ID in Windows OS. Updated package

drawing.

June 2018 1.4.1 Updated to MaxLinear logo. Updated format and Ordering Information. Removed

Windows 2000, removed IR mode from Tx and Rx pins. GPIO_INT_MASK register

logic updated. Updated all "V1410" to XR21V1410. Updated last paragraph of 

General Description. Updated GPIO_SET and GPIO_CLEAR Register Descriptions.

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transmitted in any form or by any means (electronic, mechanical, photocopying, recording, or otherwise), or for any purpose, without the express written permission of MaxLinear, Inc.

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assurances to its satisfaction that: (a) the risk of injury or damage has been minimized; (b) the user assumes all such risks; (c) potential liability of MaxLinear, Inc. is adequately

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Company and product names may be registered trademarks or trademarks of the respective owners with which they are associated.

XR21V1410

REV. 1.4.1 1-CH FULL-SPEED USB UART

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