AN2327 - Freescale Semiconductor / Motorola

The Motorola enhanced background debug interface (EBDI) provides a cost effective

background debug mode (BDM) interface to the Motorola M•Core and CPU32

microcontrollers. In order to provide a reliable BDM connection, there are some hardware

design considerations and target system requirements that need to be observed. This document

discusses these requirements as they pertain to the M•Core family of devices.

1. ONCE Module

The M•Core ONCE module provides a mechanism for code debugging and run-time control,

without utilising any of the MCU resources. Hardware breakpoints built into the MCU allow

code to be debugged even when residing within the internal device Flash.

The M•Core ONCE module consists of a state machine that is clocked from an external source

such as the EBDI. This is asynchronous to the MCU core while internal logic ensures that all

core/ONCE block data transfers are synchronised. Data is serially shifted between the EBDI

and ONCE block using 2 data pins.

For more information on the ONCE debug interface, refer to the appropriate

implementation-specific user’s manual.

2. EBDI

The EBDI, shown in Figure 1, connects to any standard PC RS232 serial connection. An

external 5v power supply is required if the voltage of the target system is less than 5 volts.

Figure 1. EBDI Interface Box

Application Note

AN2327/D

Rev. 0, 9/2002

M•Core EBDI Interface

Application Note

Alasdair Robertson

TECD Applications,

Scotland

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2M•Core EBDIInterfaceApplicationNote MOTOROLA

ONCE Signal Routing

The latest EBDI, part number MMC14EBDI02, supports the following M•Core devices:

• MMC2001

• MMC2080

• MMC2102

• MMC2103

• MMC2107

•MMC2111

• MMC2114 (requires the latest firmware)

• MMC3401 (without Nexus)

The firmware on EBDI revisions E and G is software re-programmable. For the latest firmware versions and

for information on the current devices supported, refer to

http://e-www.motorola.com/webapp/sps/site/prod_summary.jsp?code=MMC14EBDI02.

3. Target System Design Considerations

In order to physically connect the EBDI to the target system, a 2 x 7 way, 0.1 inch pitch connector is

required. The pinout for this connector is shown in Figure 2. Note that pin 8 is not connected and serves as

a polarisation pin. The EBDI cable has the socket at position 8 closed off and, on the target system, this pin

should be physically removed from the header.

Figure 2. ONCE Connector Pinout

3.1 ONCE Signal Routing

It is critical that there are no glitches on the ONCE control signals because they can cause the ONCE state

machine to enter an incorrect state and disrupt communication with the EBDI. Similarly, any signal

problems on the TDI/TDO signals can result in incorrect data transmission.

It is usually desirable to locate the ONCE connector at the edge of the PCB for easy connectivity with the

EBDI; however, care should be taken to ensure that the track length between the connector and MCU is

minimised. While the track length is not critical, longer tracks will result in possible signal degradation and

unreliable ONCE operation. Low-impedance tracking should be used.

Table 1 shows specific routing instructions for the ONCE signals. They should all be connected to 3.3 volts

(or the ONCE pad voltage) via 10KΩpullup resistors.

2GND

4GND

6GND

8 Removed Pin

10 TMS

12 DBEV

14 TRST

TDI 1

TDO 3

TCLK 5

GPI 7

RESET 9

VDD111

GPO 13

Notes:

1ONCE Pin pad voltage, typically +3.3v

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MOTOROLA M•Core EBDIInterfaceApplicationNote 3

ONCE Operation

3.2 ONCE Operation

As previously mentioned, the EBDI does not implement the DBEV signal to place the M•Core into

background debug mode. Instead, it asserts the MCU reset and then sends a command stream to the ONCE

module (including assertion of TRST) to initiate BDM mode. The MCU reset is then released and the MCU

can be controlled via the EBDI. The oscilloscope traces in Figure 3 show the reset sequence.

Table 1. Routing Instructions for ONCE Signals

Signal Instructions

TDI/TDO Test Data In/Out. Connect to corresponding signals on the MCU.

DBEV Debug Event. Connect to the MCU DBEV signal. This signal is not driven by the EBDI and MUST be

tied high to ensure that the MCU does not enter background mode unexpectedly.

GPI/GPO These signals are not routed to the MCU and should be pulled to 3.3 volts at the ONCE connector using

10K resistors.

RESET ONCE Reset. Connect to the MCU Reset-In pin. Note that if there are multiple sources of reset

connected to the Reset-In pin, it is recommended that they be gated together; otherwise, conflicts may

occur in the case of non-open drain outputs and the EBDI, for example, would not be able to reset the

MCU.

TRST Test Access Port Reset. Connect to the MCU TRST pin.

TMS Test Mode Select. Connect to the MCU TMS pin.

TCLK Test Clock. Connect to the MCU TCLK pin. In order to reduce the harmonics and, therefore, the effect

on EMI, a 47pf capacitor should be placedbetween this signaland the board ground plane, close to the

ONCE connector. The signal quality can be further improved byplacing a lowvalue terminationresistor

on the TCLK line after it has gone to the MCU. Care should be taken to ensure that low impedance

tracking is used on the TCLK signal to increase signal integrity.

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4M•Core EBDIInterfaceApplicationNote MOTOROLA

ONCE Operation

Figure 3. ONCE Reset Sequence

If any communication problems are encountered when using the EBDI, check that the reset sequence is as

shown in Figure 3. As previously mentioned, any glitches on these signals can cause the ONCE module to

lose communication with the EBDI.

The traces in Figure 4 show a typical memory read via ONCE. Note the data on the TDO and TDI lines. The

EBDI only clocks the TCLK signal when communication is in progress. This differs from some of the other

BDM interfaces that continually clock the TCLK line.

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MOTOROLA M•Core EBDIInterfaceApplicationNote 5

Target System Memory Map

Figure 4. ONCE Data Read

4. Operational Requirements

This section details the target and configuration requirements for successful use of the EBDI

4.1 Target System Memory Map

As part of it’s initialisation process, the EBDI reads target system memory at address 0x0. If the EBDI

cannot read from 0x0, it’s ONCE algorithms will not be correctly initialised and it will not function. The

memory at address 0x0 can be RAM or Flash/ROM as long as it can be successfully read.

This presents a problem for some M•Core parts that utilise a bootloader to configure the device from reset.

Typically, this bootloader would be responsible for enabling the internal device Flash, normally located at

address 0x0. A workaround for this is to allow the EBDI to reset the device as normalbut immediately return

control to the bootloader for a few seconds before the EBDI attempts to fully initialise the ONCE module.

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6M•Core EBDIInterfaceApplication Note MOTOROLA

TCLK Frequency

This workaround is controlled in the debugger startup script. An example for the SDS debugger follows:

go -n # Return control to bootloader

sleep 5 # Wait 5 seconds

stop # Debugger interrupts bootloader and stops code execution.

These commands should be placed at the very start of the configuration file so they are the first user

commands executed after reset.

NOTE

The reset configuration word settings may require alteration to allow

memory to be available or the bootloader to run from reset.

4.2 TCLK Frequency

The TCLK frequency must be less than ¼ of the MCU system clock. This is typically controlled as

a configuration setting in the debugger.

4.3 Debugger Support

The EBDI for M•Core is currently supported by the following debuggers:

• WindRiver Single Step www.windriver.com

• Metrowerks CodeWarrior www.metrowerks.com

NOTE

The EBDI uses a software interface library (ESL) to interact with the

debugger and, as such, the debugger does not directly control the EBDI,

but uses the EBDI function calls.

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7M•Core EBDIInterfaceApplication Note MOTOROLA

Debugger Support

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AN2327/D

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