CMX269A データシートの表示（PDF） - MX-COM Inc

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CMX269A

1200/2400/4800bps MSK Modem

MX-COM Inc  

1200/2400/4800bps MSK Modem

7

CMX469A PRELIMINARY INFORMATION

Recommended External Component Notes:

1. VBIAS may be bypassed to VSS and VDD using C2 and C6 when input signals are referenced to the

VBIAS pin. For input signals references to VSS, bypass VBIAS to VSS using C2 only.

2. The performance of the Carrier Detect function will be affected by the nature of the noise spectrum in

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.

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

least 40% of VDD, peak to peak. Tuning fork crystals generally cannot meet this requirement. To

obtain crystal oscillator design assistance, consult your crystal manufacturer.

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 Tx Enable low. Serial data applied to Tx Data Input is sampled internally

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.

©1999 MX-COM, Inc.

www.mxcom.com tel: 800 638 5577 336 744 5050 fax: 336 744 5054

Doc. # 20480191.002

4800 Bethania Station Road, Winston-Salem, NC 27105-1201 USA

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