Baseband Processor For Mixed Mode Land Mobile Radio
CMX880
3, …” and in the FFSK case an innocuous bit sequence may be all ‘1’s. The modulator outputs can be ramped
down whilst transmitting this data padding.
Voice data is the sampled voice data to be output to the audio output during a voice based signal reception or is
the sampled voice data to drive the modulator outputs during a voice based signal transmission.
It is recommended that the symbol stream for transmitting C4FM or CQPSK utilises the Fast Serial Bus
interface, rather than the “C-BUS” interface.
$C5 RX DATA: 16-bit read-only
15
14
13
12
MS Data Byte
Bit 4 Bit 3
11
10
9
8
7
6
5
4
3
2
1
0
Bit:
FFSK/MSK
LS Data Byte
Bit 4 Bit 3
Bit 7
Bit 6
Bit 5
Bit 2
Bit 1
Bit 0
Bit 7
Bit 6
Bit 5
Bit 2
Bit 1
Bit 0
C4FM/
CQPSK
VOICE
Symbol 1
Bit 1 Bit 0
2s complement
Symbol sample quality data
2’s complement encoded voice data
Symbol 0
2s complement
Symbol sample quality data
Bit 1 Bit 0
This word holds either the last 16 bits of received and decoded FFSK/MSK data, the last 2 decoded C4FM
symbols or the most recently received Voice signal level. The MS bit of the FFSK/MSK data is received first.
The most significant symbol of C4FM data is received first.
FFSK/MSK is transferred synchronously, so incoming FFSK/MSK data is decoded as a continuous stream of
bits, with no detection of start, stop or parity bits and no CRC checking. If data is not read before the next 16
bits of data are received and decoded, the old data will be overwritten with the new data.
Voice data is the voice input from the selected microphone input during transmission, or the extracted (by band
pass filtering) voice signal from the FM discriminator input during receive.
It is recommended that the symbol stream from the C4FM receiver utilises the Fast Serial Bus interface, rather
than the “C-BUS” interface.
ã 2001 Consumer Microcircuits Limited
48
D/880/1
CMLMICRO [ CML MICROCIRCUITS ]
