Baseband Processor For Mixed Mode Land Mobile Radio
CMX880
1.5.2.2
FSB Register Description
The FSB Data Word Format is dependent on the CMX880 mode of operation. The six main applications of the
FSB are to transfer data between the CMX880 and the DSP:
·
·
·
·
·
·
.
‘transmit C4FM/CQPSK symbol data’ from the DSP to the CMX880,
‘received C4FM symbol data’ from the CMX880 to the DSP,
‘Voice data (from Microphone or FM Discriminator input ports)’ from the CMX880 to the DSP,
‘Voice data (to Modulator or Audio output ports)’ from the DSP to the CMX880,
‘FFSK data’ from the CMX880 to the DSP,
‘FFSK data’ from the DSP to the CMX880.
C4FM/CQPSK Transmit Symbol Data
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
Bit:
Symbol 7
Symbol 6
Symbol 5
Symbol 4
Symbol 3
Symbol 2
Symbol 1
Symbol 0
Bit
1
Bit
0
Bit
1
Bit
0
Bit
1
Bit
0
Bit
1
Bit
0
Bit
1
Bit
0
Bit
1
Bit
0
Bit
1
Bit
0
Bit
1
Bit
0
This word holds the next 8 C4FM/CQPSK symbols to be transmitted. The most significant symbol of
C4FM/CQPSK data is transmitted first. Symbols beyond the actual data message length should be padded with
innocuous values. The modulator outputs can be ramped down whilst transmitting this data padding.
C4FM Receive Symbol Data
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
Bit:
Symbol 1
2s complement
Symbol sample quality data
Symbol 0
2s complement
Symbol sample quality data
Bit
1
Bit
0
Bit
1
Bit
0
This word contains the last 2 decoded C4FM symbols. The MS bit is received first.
Sampled Symbol Level
Bit 1
Bit 0
+3
+1
-1
0
0
1
1
1
0
0
1
-3
The 2s complement ‘Symbol Sample Quality Data’ represents the deviation of the sampled level from the
perceived ideal sample level.
Range :
- 1.0 to +0.96875 of the unit symbol level.
Resolution :
0.03125 of the unit symbol level per LSB.
If the scaled sample level is greater than +3.96875, a +3 symbol level is decoded with the sample error capped
at +0.96875. Likewise if the scaled sample level is less than –4.0, a -3 symbol level is decoded with the sample
error capped at –1.0.
ã 2001 Consumer Microcircuits Limited
65
D/880/1
CMLMICRO [ CML MICROCIRCUITS ]
