CMX881 查看數據表（PDF） - CML Microsystems Plc

零件编号

产品描述 (功能)

生产厂家

CMX881

Baseband Processor for PMR and Trunked Radios

CML Microsystems Plc 

PMR Signalling Processor

CMX881

1.5.3 Receive Mode

The CMX881 can receive voice and various signal formats: CTCSS tone, DCS code, Selcall and FFSK/

MSK data at 1200 and 2400bps. Reception of each of these signal types can be independently

enabled/disabled by C-BUS command. If enabled, an interrupt will be issued to notify the host µC of the

presence and type of the incoming signal.

In receive mode the CMX881 performs signal type identification in 2 frequency bands, sub-audio (60 -

260Hz) and voice band (300 - 3kHz), to determine what type of signal is being received. When an

enabled signal is detected this will be indicated to the host over the C-BUS and the CMX881 will continue

to process the received signal in its band. Identification / process mode will continue in the other band.

The CMX881 can process voice and simultaneously identify and process at least 2 other signal types

(one in the sub-audio in parallel with one in the voice band). See Table 1 for valid combinations.

The receive gain and audio output amplifier gain can be adjusted by the host µC, via C-BUS command,

to provide receive signal level adjustment and output volume control or muting.

Table 1 Concurrent Rx Signalling Modes Supported by the CMX881

With Rx Voice

Processing1 or

Audio Tone

generation

Sub-Audio

All combinations of:

DCS

Inverted DCS

CTCSS

Voice band signalling

Any one of A - E:

A None

B 1200bps FFSK/MSK

C 2400bps FFSK/MSK

D 1200 & 2400 bps FFSK/MSK

E Selcall

No Voice

Processing or

Audio Tone

generation

Sub-Audio

All combinations of:

DCS

Inverted DCS

CTCSS

1 Including optional de-emphasis

Voice band signalling

All combinations of:

Selcall

1200bps FFSK/MSK

2400bps FFSK/MSK

By disabling all the decoding modes, the device can be configured to receive voice only signals with no

decoding of the voice band, CTCSS or DCS signalling. This will result in reception of all signals as if

they are voice. In this case it is up to the user/host µC to respond appropriately to incoming signals.

The CMX881 operates in half duplex, so whilst in receive mode the transmit path (microphone input and

modulator output amplifiers) can be disabled and powered down if required. The AUDIO output signal

level is equalised (to VBIAS) before switching between the audio port and the modulator ports, to minimise

unwanted audible transients. The Off/Power-save level of the modulator outputs is the same as the

VBIAS pin, so the audio output level must also be at this level before switching.

 2004 CML Microsystems Plc

15

D/881/7

Share Link: