CMX269AE2 MX-COM, Inc., CMX269AE2 Datasheet - Page 7

• Manufacturer Part Number: CMX269AE2
• Description: 1200/2400/4800bps MSK modem
• Manufacturer: MX-COM, Inc.

1200/2400/4800bps MSK Modem
Recommended External Component Notes:
4. General Description
The CMX469A has two sections, apart from the Xtal oscillator circuit and clock dividers. These sections may
be independently powersaved.
4.1 Transmitter
The transmitter is enabled by taking
and an MSK sequence is generated. After filtering, this is output at Tx Signal Out and the transmit clock
derived from this signal is output at Tx Sync Out.
The Tx Data must be valid at the time of the rising edge of the Tx Sync clock signal. Therefore, the optimum
time to change Tx Data is on the falling edge of the Tx Sync clock.
4.2 Receiver
The receiver is enabled by taking Rx Enable high. The signal applied to Rx Signal In is filtered and recovered
as serial data from the Unclocked Data Out. A flywheel synchronizer is used to extract a clock from the
recovered serial data stream. The clock is available at Rx Sync Out and the retimed serial data is available at
Clocked Data Out. The optimum time to sample the Clocked Data Out is on the falling edge of the Rx Sync
Out clock signal.
The integrated peak values of the Rx Amplitude are compared with out-of-band noise levels and used to
make a signal-to-noise assessment, which is available at Carrier Detect Out.
A Bandpass output is also available from the output of the first Rx filter stage, but will require buffering before
use.
4800 Bethania Station Road, Winston-Salem, NC 27105-1201 USA
1999 MX-COM, Inc.
1. V
2. The performance of the Carrier Detect function will be affected by the nature of the noise spectrum in
3. A 4.032MHz Xtal/Clock is required for 4800 baud operation.
4. For best results, a crystal oscillator design should drive the clock inverter input with signal levels of at
V
the received channel. The value of C4 determines the Carrier Detect time constant. A long time
constant results in improved noise immunity but increased response time. C4 may be varied to trade-
off response time for noise immunity.
least 40% of V
obtain crystal oscillator design assistance, consult your crystal manufacturer.
BIAS
BIAS
may be bypassed to V
pin. For input signals references to V
DD
, peak to peak. Tuning fork crystals generally cannot meet this requirement. To
www.mxcom.com tel: [phone] 744 5050 fax: [phone]
SS
Tx
and V
Enable
DD
using C2 and C6 when input signals are referenced to the
low. Serial data applied to Tx Data Input is sampled internally
SS
, bypass V
7
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BIAS
to V
SS
CMX469A PRELIMINARY INFORMATION
using C2 only.
Doc. # 20480191.002