FX809
FFSK Modem
Fig 1. FX809 FFSK Modem
Brief Description
An intelligent, half-duplex, FFSK/MSK modem which
operates under “C-BUS” control. In addition this
modem provides software selectable checksum
generation and error checking, in accordance with
MPT1327.
The FX809, using Interrupt and Status Register
procedures, performs the functions described below:
In Tx mode the FX809 will:
1. (a) Accept from the host and transmit, 8-bit bytes
of data as instructed (Preamble, Sync, Address
and data).
(b) internally calculate and insert a 2 byte
checksum based upon the preceeding 6 bytes of
data, or
(c) disable the internal checksum generator and
continuously transmit the data supplied.
2. Transmit 1 hang-bit and go to Tx Idle when all
loaded data bytes have been transmitted.
In Rx mode the FX809 will:
1. Detect and achieve bit synchronization within 16
bits.
2. (a) Search and detect the user-programmed Sync
(or its opposite logic sense) Word and achieve
frame sychronization. Data will then be output in
8-bit bytes via the Rx Data Buffer.
Rx IN
SERIAL
CLOCK
COMMAND
DATA
CHECKSUM
GEN/CHECK
INTERRUPT
GENERATOR
ADDRESS
SELECT
TX OUT
Recovered
Clock
FFSK
TRANSMITTER
Recovered
Clock
8-Bit Parallel Bus
FFSK
RECEIVER
XTAL/CLOCK
CLOCK
GENERATOR
STATUS
REGISTER
UNCOMMITTED
AMPLIFIER
AMP
IN
AMP
OUT
REPLY
DATA
C-BUS
INTERFACE
AND
CONTROL
LOGIC
SYNC/SYNC
DETECT
TX DATA BUFFER
RX DATA BUFFER
DATA REGISTER 1 DATA REGISTER 2
–
+
Rx SYNC
Detect
BYTE
COUNTER
Rx Data
Ready Tx Data
Ready Tx Idle
VBIAS
VBIAS
VSS
VDD
Interrupt
Enable
Rx SYNC
Detect
ADDRESS
DECODER
Rx FREE FORMAT
CONTROL
REGISTER
Rx SYNC
Detect
Rx SYNC
Detect
XTAL
WAKE
CS
SYNC PROGRAM
LOW – HIGH
IRQ
(b) Use the received checksum to calculate the
presence of any errors, setting the Status
Register accordingly.
3. Make the incoming data directly available, via the
Rx Data Buffer (Rx Freeformat), overriding
synchronization requirements.
The FX809 achieves Rx input timing by recovering
an Rx clock from the incoming data stream. Output
tones are timed to the internally generated transmit
clock. Filter, register clocks and transmit FFSK tone
frequencies are derived internally from the external
Xtal or clock pulse input.
For compliance with the MPT 1327 Signalling
Specification a 4.032MHz Xtal or clock input will be
required.
NOTE: All information contained in this data sheet is
specified using a 4.032 MHz Xtal, 1200 bps baud rate ,
Mark and Space frequencies 1200 Hz and 1800 Hz.
The FX809 is a low-power 5-volt integrated circuit,
incorporating “Powersave” modes to further reduce
power requirements.
An uncommitted amplifier is provided on chip for
general purpose applications within DBS 800.
The FX809 is available in 24-pin cerdip DIL and 24-
pin/lead plastic SMD packages.
Publication D/809/5 April 1998
Pin NumberFunction
FX809
J/LG/LS
1
2
3
4
5
6
7
8
9
10
11
12
Xtal: The output of the on-chip clock oscillator. External components are required at this input
when a Xtal input is used. See Figure 2, INSET.
Xtal/Clock: The input to the on-chip clock oscillator inverter. A Xtal or externally derived clock
should be connected here. See Figure 2, INSET.
Interrupt Request (IRQ): The output of this pin indicates an interrupt condition to the
µController, by going to a logic “0.” This is a “wire-or able” output, enabling the connection of
up to 8 peripherals to 1 interrupt port on the µController. This pin has a low-impedance
pulldown to logic “0” when active and a high-impedance when inactive. The system IRQ line
requires a 'pull-up' resistor to VDD.
The conditions that cause interrupts are indicated in the Status Register and are shown below:
Tx Idle Rx Data Ready Tx Data Ready
Rx SYNC Detect Rx SYNC Detect
Interrupt outputs can be disabled by bit 3 of the Control Register.
No Internal connection.
No Internal connection.
Rx Freeformat: Used in the Rx mode, this input, when a logic “0,” allows received data to be
read from the Rx Data Buffer via the Reply Data line without having to acheive byte
synchronization (SYNC/SYNC) first. Data will continue to be available after this input goes to a
logic “1” until either a SYNC or SYNC Prime bit is set or the the modem set to Tx mode.
When held at a logic “1” the modem operates normally. This pin has an internal 1MΩ pullup
resistor.
NOTE: If this input is held at a logic “0” in the Tx mode, the Rx Data Ready bit in the Status
Register may occasionally be set, but not cause an interrupt. If this input is a logic “0” when
going into the Rx mode, an Rx Data Ready interrupt may be generated immediately, in this
case the first byte of Rx data should be ignored.
VBIAS : The internal circuitry bias line, held at VDD/2 this pin must be decoupled to VSS by
capacitor C3, see Figure 2.
Amp In: The inverting input to the on-chip uncommitted amplifier .
Amp Out: The output of the on-chip uncommitted amplifier.
Rx In: The 1200 baud, 1200Hz/1800Hz, received FFSK signal input. The input signal to this
pin must be a.c. coupled via capacitor C4, see Figure 2.
No Internal connection.
VSS: Negative Supply (GND).
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
10 -5
10 -2
10 -3
10 -4
Signal to Noise Ratio (dB) [Bit-Rate Bandwidth]
Bit Error Rate
(Logarithmic Scale)
Ideal Coherent FFSK
Characteristic
2 x 10
-2
2
4
6
3
8
FX809
Characteristic
(Linear Scale )
Fig.3 Bit Error Rate vs Signal-to-Noise Ratio
VBIAS
XTAL/CLOCK
VDD
13
14
15
16
17
18
19
20
21
22
23
241
2
3
4
5
6
7
8
9
10
11
12
FX809J
VSS
VDD
Tx OUT
SEE INSET XTAL
VSS
Rx FREEFORMAT
SIGNAL OUT Rx IN
REPLY DATA
SERIAL CLOCK
CS
COMMAND DATA
ADDRESS SELECT
WAKE
2
1
XTAL/CLOCK
XTAL
VSS
INSET
FX809J
R1
C1
C2
C3
C4
C5
IRQ
X1
R4
SIGNAL IN
C7
R2 C6 R3
External Components
Modem Performance
Component Value
R1= 1.0MΩ
R2Note 1
R3100kΩ
R422.0kΩ
C133.0pF
C233.0pF
C31.0µF
C40.1µF
C51.0µF
C633.0pF
C7Note 1
X14.032MHz
Tolerance: R = ±10% C = ±20%
Fig.2 External Components
Note 1:
R2, R3 and C7 form the gain
components for the signal;
R3 should be chosen as
required by the signal input
level.
Handling Precautions
The FX809 is a CMOS LSI circuit which includes input
protection. However precautions should be taken to
prevent static discharges which may cause damage.
CML does not assume any responsibility for the use of any circuitry described. No circuit patent licences are implied
and CML reserves the right at any time without notice to change the said circuitry.
Ordering Information
FX809J 24-pin cerdip DIL (J4)
FX809LG 24-pin encapsulated bent and
cropped (L1)
FX809LS 24-lead plastic leaded chip
carrier (L2)
Package Outlines
The FX809 is available in the package styles outlined
below. Mechanical package diagrams and specifications
are detailed in Section 10 of this document.
Pin 1 identification marking is shown on the relevant
diagram and pins on all package styles number
anti-clockwise when viewed from the top.
NOT TO SCALE
Max. Body Length 10.25mm
Max. Body Width 10.25mm
FX809LG 24-pin quad plastic encapsulated
bent and cropped (L1)
FX809J 24-pin cerdip DIL (J4)
NOT TO SCALE
Max. Body Length 10.40mm
Max. Body Width 10.40mm
FX809LS 24-lead plastic leaded chip carrier
(L2)
NOT TO SCALE
Max. Body Length 32.03mm
Max. Body Width 14.81mm
CML Product Data
In the process of creating a more global image, the three standard product semiconductor
companies of CML Microsystems Plc (Consumer Microcircuits Limited (UK), MX-COM, Inc
(USA) and CML Microcircuits (Singapore) Pte Ltd) have undergone name changes and, whilst
maintaining their separate new names (CML Microcircuits (UK) Ltd, CML Microcircuits (USA)
Inc and CML Microcircuits (Singapore) Pte Ltd), now operate under the single title CML Micro-
circuits.
These companies are all 100% owned operating companies of the CML Microsystems Plc
Group and these changes are purely changes of name and do not change any underlying legal
entities and hence will have no effect on any agreements or contacts currently in force.
CML Microcircuits Product Prefix Codes
Until the latter part of 1996, the differentiator between products manufactured and sold from
MXCOM, Inc. and Consumer Microcircuits Limited were denoted by the prefixes MX and FX
respectively. These products use the same silicon etc. and today still carry the same prefixes.
In the latter part of 1996, both companies adopted the common prefix: CMX.
This notification is relevant product information to which it is attached.
Company contact information is as below:
CML Microcircuits
(UK)Ltd
COMMUNICATION SEMICONDUCTORS
CML Microcircuits
COMMUNICATION SEMICONDUCTORS
CML Microcircuits
(Singapore)PteLtd
COMMUNICATION SEMICONDUCTORS
CML Microcircuits
(USA) Inc.
COMMUNICATION SEMICONDUCTORS
Oval Park, Langford, Maldon,
Essex, CM9 6WG, England
Tel: +44 (0)1621 875500
Fax: +44 (0)1621 875600
uk.sales@cmlmicro.com
www.cmlmicro.com
4800 Bethania Station Road,
Winston-Salem, NC 27105, USA
Tel: +1 336 744 5050,
0800 638 5577
Fax: +1 336 744 5054
us.sales@cmlmicro.com
www.cmlmicro.com
No 2 Kallang Pudding Road, 09-05/
06 Mactech Industrial Building,
Singapore 349307
Tel: +65 7450426
Fax: +65 7452917
sg.sales@cmlmicro.com
www.cmlmicro.com
D/CML (D)/1 February 2002
