CMX881(2002) 查看數據表（PDF） - CML Microsystems Plc

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CMX881
(Rev.:2002)

Baseband Processor for PMR and Trunked Radios

CML Microsystems Plc 

PMR Signalling Processor

CMX881

DCS

The DCS code is in NRZ format and is transmitted at 134.4b/s in either 23 or 24 bit patterns. The code,

for transmission or reception is programmed via the host µC with the ‘turn-off’ code being supplied from

the CTCSS facility. Decoding is carried out rapidly thus avoiding the loss of the beginning of speech or

data signals.

Selcall

This product implements a fully programmable Selcall encoder and decoder employing normal and

special tones. Tone frequencies, decoder bandwidths and thresholds are programmed by the host µC. In

receive the CMX881 scans its internal tone table for a match, reporting its results to the µC.

FFSK/MSK Data

A free-format half duplex FFSK/MSK modem. In receive this device can decode data at either automatic

or manually selected 1200b/s or 2400b/s rates. Additionally, in receive, a 16-bit programmed frame sync

(MPT packet-type) pattern can be detected. Data and formatting to and from the modem is under the

control of the host µC.

DTMF Tx

The CMX881, under µC control, can generate and transmit all standard DTMF tone-pairs.

Signal Monitor

An auxiliary circuit intended for the monitoring of any signal or level; both internal and external. This

function can be used in conjunction with the host µC to allow such activities as: VOX operation and/or the

‘wake-up’ of powered-down circuitry.

Audio Processing:

Adjustable Gain Input Amplifiers

Selectable, component adjustable inputs are available for microphone or line voiceband or discriminator

inputs. In either mode (Tx or Rx) the selected input can be further level adjusted under the control of the

host µC prior to signal- or audio- processing.

Voiceband and Sub-Audio Filtering with Limiting

Both Rx and Tx paths present voiceband filtering; the Tx path filter can be configured to either 12.5 or 25

kHz channel spacing whilst the Rx path also includes a sub-audio passband filter.

Voiceband Pre-emphasis and De-emphasis

Voiceband pre-emphasis is selectable to either 12.5 or 25 kHz channel configurations in the Tx path; de-

emphasis at -6dB/ octave is selectable in the Rx path.

Software Adjustable Gains, Volume, Mixing and Routing

Providing total flexibility of operation, this product, under µC control has the ability to select and route

functions and audio and signal paths, set bandwidths and threshold levels, mix audio and sub bands and

vary both input and out gain/attenuation levels. Output levels from all analogue ports can be ‘ramped’ up

and down at independently programmed rates.

Attenuation-Adjustable Single/Two-Point Modulation Outputs

To facilitate a wide range of transmitter types, the CMX881 has the ability to provide, independently

programmable, modulation outputs; for single or two-point modulation schemes.

© 2002 CML Microsystems Plc

3

D/881/2

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