Baseband Processor For Mixed Mode Land Mobile Radio
CMX880
If DCS Inverse bit 15 = 1, DCS will be transmitted such that a DCS ‘1’ will generate a –ve voltage swing (below
) and a DCS ‘0’ will generate a +ve voltage swing (above V ). If DCS Inverse bit 15 = 0, DCS will be
V
BIAS
BIAS
transmitted such that a DCS ‘1’ will generate a +ve voltage swing (above V
) and a DCS ‘0’ will generate a -
BIAS
ve voltage swing (below V ). See Table 4 DCS Modulation Modes.
BIAS
Bit 11
Bit 10
Bit 9
0
0
0
1
X
0
0
1
0
X
0
1
0
0
X
No In-Band (Voice) Signalling Transmitted
FFSK/MSK Transmit
DTMF Tones Transmit
Selcall Tone Transmit
Do not use other code combinations.
If FFSK/MSK is enabled, the baud rate is controlled by bit 8, ‘2400baud’. If bit 8 = 0, 1200baud will be selected;
if bit 8 = 1, 2400baud will be selected.
The voice filter control bits determine the filter mode applied to the voice or In-Band tone signal before it is
transmitted. Pre-emphasis can be applied without other filtering by setting bits 5, 4, 3 = 0, 0, 1.
Bit 5
Bit 4
Bit 3
0
X
0
1
1
1
0
X
1
0
1
1
0
1
X
X
0
1
No filtering.
Enable pre-emphasis.
12.5kHz channel filtering.
25.0kHz channel filtering.
APCO 25.
Reserved – do not use.
The C4FM/CQPSK select bits determine which digital transmit mode is to be transmitted, if any. If voice is being
encoded and transmitted, bit 14, ‘Voice Enable’ should be set to 1, bits 5 to 7 should select APCO 25. If data is
being transmitted ‘Voice Enable’ should be cleared to 0.
Bit 7
Bit 6
0
0
1
1
0
1
0
1
C4FM AND CQPSK TX OFF
C4FM
CQPSK
Reserved – do not use.
If transmitting using C4FM or CQPSK, bits 9 to 13 must all be 0. Likewise if transmitting on an analogue
channel, bits 6 and 7 must both be 0.
ã 2001 Consumer Microcircuits Limited
53
D/880/1
CMLMICRO [ CML MICROCIRCUITS ]
