Baseband Processor For Mixed Mode Land Mobile Radio
CMX880
Voice Data
Bit:
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
2’s complement encoded voice data
This word holds the next voice signal to the DAC path. This is sampled voice data to be output to the audio
output during a voice based signal reception or to drive the modulator outputs during a voice based signal
transmission.
This word holds the current sampled and filtered voice signal from the ADC path. This may be 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.
FFSK Data
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
Bit:
FFSK/MSK
MS Data Byte
LS Data Byte
Bit
7
Bit
6
Bit
5
Bit
4
Bit
3
Bit
2
Bit
1
Bit
0
Bit
7
Bit
6
Bit
5
Bit
4
Bit
3
Bit
2
Bit
1
Bit
0
This word holds the next 2 bytes of FFSK/MSK data or the next 8 C4FM/CQPSK symbols to be transmitted.
Outgoing data is treated as continuous. If new data is not provided before the current data has been
transmitted, the current data will be re-transmitted, until new data is provided. Transmission of the current word
of data will be completed before transmission of the new data begins.
Data Padding
The most significant bit of FFSK/MSK data is transmitted first. The most significant symbol of C4FM/CQPSK
data is transmitted first. Bits or symbols beyond the actual data message length should be padded with
innocuous values (system dependent). In the C4FM case an innocuous symbol sequence may be “+3, +3, -3, -
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.
ã 2001 Consumer Microcircuits Limited
66
D/880/1
CMLMICRO [ CML MICROCIRCUITS ]
