1200/2400bps MSK Modem for Trunked Radio Systems
3
MX429A
1 Block Diagram
CARRIER DETECT
TIME CONSTANT
DATA
RX MESSAGE FORMAT
RX CHECKSUM TRUE
RECEIVER INPUT
1200/2400 BAUD
MSK
SYNC/SYNT
DETECTOR
BYTE
CHECKSUM
CHECKER
RECEIVER
COUNTER
STATUS
REGISTER
SYNC
RECOVERED CLOCK
MICROPROCESSOR
INTERFACE
STROBE
R/W
A1
RX DATA
REGISTER
SYNT
RX CARRIER
DETECT
DATA
RX DATA READY
8-BIT uP BUS
RX CARRIER DET.
RX CHECKSUM TRUE
TX DATA READY
TX IDLE
RX DATA
BUFFER
A0
D7
D6
D5
D4
D3
8-BIT uP BUS
TX DATA
BUFFER
TIMER EXPIRED
CONTROL
REGISTER
CHECKSUM
GENERATOR
D2
D1
D0
TX PARITY
ENABLE
RX ENABLE
TX ENABLE
RX MESSAGE FORMAT
TX PARITY ENABLE
TX DATA
REGISTER
V
BIAS
TRANSMITTER
OUTPUT
CLOCKS
V
V
SS
DD
MSK
TRANSMITTER
BYTE
COUNTER
XTAL/CLOCK
XTAL
RX DATA RDY
CLOCK
GENERATORS
TX DATA RDY
SYNC
IRQ
INTERRUPT
GENERATOR
TIMER
SYNT
TX IDLE
1.008 MHz
OUTPUT
Figure 1: Block Diagram
2 Signal List
Pin No.
Signal
Description
The internal circuitry bias line, held at V /2 this pin must be
J/P LH
Name
Type
1
1
V
BIAS
DD
decoupled to V by a capacitor, see Figure 2.
SS
2
2
Transmit Output
Receiver Input
Output The 1200 baud, 1200Hz/1800Hz and 2400 baud, 1200Hz/2400Hz
MSK Tx output. When not enabled by the Control Register (D0) its
output impedance is set high.
3
5
4
5
Input
The 1200/2400 baud received MSK signal input. The
1200Hz/1800Hz, 1200Hz/2400Hz audio to this pin must be ac
coupled via a capacitor, see Figure 2.
V
DD
Power Positive Supply. A single +5V regulated supply is required. It is
recommended that this power rail be decoupled to V by a
SS
capacitor, see Figure 2.
6
7
8
6
7
8
Carrier Detect
Time Constant:
The on-chip Carrier Detect function requires external
component(s) on this pin. See Figure 2for recommended
component(s).
Xtal/Clock
XTAL
The input to the clock oscillator inverter. A 4.032 MHz Xtal or
externally derived clock pulse input should be connected here,
see Figure 2.
The output of the 4.032 MHz clock oscillator.
© 1998 MX-COM Inc.
www.mxcom.com Tel: 800 638-5577 336 744-5050 Fax: 336 744-5054
Doc. # 20480128.007
4800 Bethania Station Road, Winston-Salem, NC 27105-1201 USA
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