CML Microcircuits
COMMUNICA
TION SEMICONDUCTORS
D/469A/3 June 2009
CMX469A
1200/2400/4800 Baud
FFSK/MSK Modem
Applications
•
•
•
•
•
•
Data-Over Radio
Personal/Cordless Telephone
Radio and General Applications
Narrowband Coax Data Channels
Two Way Radio (MPT1327) Signalling
Portable Data Terminals
Features
•
Full-Duplex FFSK/MSK Modem with
Separate Rx and Tx Enable Functions
•
Pin Selectable Data Rates:
1200, 2400 or 4800 Baud
•
Pin Selectable Xtal/Clock Inputs:
1.008MHz or 4.032MHz
•
Clock Recovery Facility
•
Carrier Detect Facility
•
Low Power Operation (2.0mA typ. at 3.0V)
1.1
Brief Description
The CMX469A is a single-chip CMOS LSI circuit which operates as a full-duplex 1200, 2400 or
4800 baud FFSK/MSK modem. The mark and space frequencies are 1200/1800, 1200/2400 and
2400/4800 Hz respectively. Tone frequencies are phase continuous; transitions occur at the zero
crossing point. A common Xtal oscillator with a choice of two clock frequencies (1.008MHz or
4.032MHz) provides baud-rate, transmit frequencies, and Rx and Tx synchronization.
The transmitter and receiver operate entirely independently, including the individual section
powersave functions. The CMX469A includes on-chip circuitry for Carrier Detect and Rx Clock
recovery, both of which are made available as output pins. Rx, Tx and Carrier Detect paths
contain bandpass filters to optimise signal conditions in each section of the modem. The
CMX469A demonstrates good sensitivity and bit-error-rate under adverse signal conditions. The
Carrier Detect time constant is set by an external capacitor, so that the product's performance can
be optimised in high noise environments. This low-power device operates from a single supply
between 2.7V and 5.5V, requires few external components and is available in a wide variety of
plastic packages.
©
2009 CML Microsystems Plc
1200/2400/4800 Baud FFSK/MSK Modem
CMX469A
CONTENTS
Section
1.0
1.1
1.2
1.3
1.4
1.5
1.6
Page
Features and Applications ..................................................................... 1
Brief Description ..................................................................................... 1
Block Diagram ......................................................................................... 3
Signal List ................................................................................................ 4
External Components ............................................................................. 6
General Description ................................................................................ 7
Application Notes.................................................................................... 8
1.6.1 Rx Enable.................................................................................... 8
1.6.2 Operational Data Rate Configurations..................................... 8
1.6.3 Test Set Up ................................................................................. 8
1.6.4 Synchronous Modem Design Considerations ........................ 9
Performance Specification................................................................... 11
1.7.1 Electrical Performance ............................................................ 11
1.7.2 Packaging ................................................................................. 17
1.7
©
2009 CML Microsystems Plc
2
D/469A/3
1200/2400/4800 Baud FFSK/MSK Modem
CMX469A
1.2
Block Diagram
Figure 1 Block Diagram
©
2009 CML Microsystems Plc
3
D/469A/3
1200/2400/4800 Baud FFSK/MSK Modem
CMX469A
1.3
Signal List
CMX469A
D3
E2
Pin
No.
1
Pin
No.
1
Signal
Name
Type
Description
CLOCK/XTAL
I/P
The input to the on-chip inverter, for use with
either a 1.008MHz or a 4.032MHz Xtal or an
external clock. Clock frequency selection is by
means of the CLOCK RATE pin. This affects the
operational data rate of the device. Operation of
any CML microcircuit without a Xtal or clock input
may cause device damage.
The output of the on-chip inverter.
A squarewave, produced on-chip, to
synchronize the input of logic data and
transmission of the FFSK/MSK signal.
When the transmitter is enabled, this pin outputs
the FFSK/MSK signal. With the transmitter
disabled, this pin is set to a high-impedance
state.
The serial logic data to be transmitted is input to
this pin.
A logic ‘0’ will enable the transmitter. A logic ‘1’ at
this input will put the transmitter into powersave
whilst forcing Tx SYNC OUTPUT to a logic ‘1’
and Tx SIGNAL OUTPUT to a high-impedance
state. This pin is internally pulled to V
DD
.
The output of the Rx Bandpass Filter. This output
impedance is typically 10kΩ and may require
buffering prior to use.
The control of the Rx function
The output of the on-chip analogue bias circuitry.
Held internally at V
DD
/2, this pin should be
decoupled to V
SS
by a capacitor (C2). This bias
voltage is maintained under all powersave
conditions.
2
3
2
3
XTALN
Tx SYNC O/P
O/P
O/P
4
5
Tx SIGNAL
O/P
O/P
5
6
7
8
Tx DATA I/P
Tx ENABLEN
I/P
I/P
7
9
BANDPASS
O/P
Rx ENABLE
V
BIAS
O/P
8
9
10
11
I/P
BI
10
11
12
12
13
14
V
SS
UNCLOCKED
DATA O/P
CLOCKED
DATA O/P
PWR
O/P
O/P
Negative supply rail (GND).
The recovered asynchronous serial data output
from the receiver.
The recovered synchronous serial data output
from the receiver. Data is latched out by the
recovered clock, available at the Rx SYNC O/P.
©
2009 CML Microsystems Plc
4
D/469A/3
1200/2400/4800 Baud FFSK/MSK Modem
CMX469A
CMX469A
D3
E2
Pin
No.
13
14
15
16
Pin
No.
15
16
18
19
Signal
Name
CARRIER
DETECT O/P
Rx SIGNAL I/P
Rx SYNC O/P
1200/2400
BAUD
SELECT
Type
O/P
I/P
O/P
I/P
Description
When an FFSK/MSK signal is being received this
output is a logic ‘1’.
The FFSK/MSK signal input for the receiver. This
input should be coupled via a capacitor, C3.
A flywheel squarewave output. This clock will
synchronize to incoming Rx FFSK/MSK data.
A logic ‘1’ on this pin selects the 1200 baud
option. Tone frequencies are: one cycle of
1200Hz represents a logic ‘1,’ one-and-a-half
cycles of 1800Hz represents a logic ‘0.’
A logic ‘0’ on this pin selects the 2400 baud
option. Tone frequencies are: one-half cycle of
1200Hz represents a logic ‘1,’ one cycle of
2400Hz represents a logic ‘0.’ This function is
also used, in part, to select the 4800 baud
option. This pin has an internal 1MΩ pullup
resistor.
17
20
4800 BAUD
SELECT
I/P
A logic ‘1’ on this pin combined with a logic ‘0’ on
the 1200/2400 BAUD SELECT pin will select the
4800 baud option (1MΩ pulldown resistor). Tone
frequencies are: one-half cycle of 2400Hz
represents a logic ‘1,’ one cycle of 4800Hz
represents a logic ‘0.’ Operation at 4800 baud is
only achieved by using a 4.032MHz Xtal or clock.
A logic input to select and allow the use of either
a 1.008MHz or 4.032MHz Xtal/clock. Logic ‘1’ =
4.032MHz, logic ‘0’ = 1.008MHz. This input has
an internal pulldown resistor (1.008MHz).
Part of the carrier detect integration function. The
value of C4 connected to this pin will affect the
carrier detect response time and hence noise
performance.
Positive supply rail. A single 2.7 to 5.0 volt
supply is required. This pin should be decoupled
to V
SS
by a capacitor (C5).
No internal connection, do not use.
18
21
CLOCK RATE
I/P
19
22
CARRIER
DETECT TIME
CONSTANT
V
DD
BI
20
24
PWR
4, 6,
17, 23
Notes:
I/P = Input
O/P = Output
BI = Bidirectional
PWR = Power
©
2009 CML Microsystems Plc
5
D/469A/3
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