PMR Signalling Processor
CMX881
code bit last. Table 4 shows a selection of valid 23-bit DCS codes, this does not preclude other codes
being programmed. Recognition of a valid DCS Code will be flagged if the decode is successful (3 or
less errors). A failure to decode is indicated by a '0' flag. This flag is updated after the decoding of every
4th bit of the incoming signal.
Once a valid DCS Code has been detected, the voice band signal can be passed to the AUDIO output
under the control of the host µC. The voice signal is extracted from the received input signal by band
pass filtering; see Figure 5.
More details for programming DCS Codes are provided in section 1.6.20.3.
The end of DCS transmissions is indicated by a 134.4 ±0.5Hz tone for 150-200ms. To detect the DCS
turn off tone while receiving DCS, the DCS turn off tone option must be selected in the Audio and CTCSS
Control ($C2) register, and, CTCSS receive must also be enabled.
When a DCS turn off tone is
detected it will cause a DCS interrupt; the receiver audio output can then be muted by the host.
Table 4 DCS 23 Bit Codes
DCS
bits
22-12
763
DCS
bits
11-0
813
815
816
819
81A
823
827
829
82C
835
839
83A
83B
83C
84C
84D
84E
855
859
85A
85C
863
86A
86D
86E
872
875
87A
DCS
bits
22-12
18B
6E9
68E
7B0
45B
1FA
58F
627
177
5E8
43C
794
0CF
38D
6C6
23E
297
3A9
0EB
685
2F0
158
776
79C
3E9
4B9
6C5
62F
DCS
bits
11-0
87C
885
893
896
8A3
8A4
8A5
8A9
8B1
8B3
8B5
8B9
8C6
8C9
8CD
8D9
8E3
8E6
8E9
8F4
8F5
8F9
909
90A
90B
913
919
91A
DCS
bits
22-12
7B8
27E
60B
6E1
3C6
2F8
41B
0E3
19E
0C7
5D9
671
0F5
01F
728
7C2
4C3
247
393
22B
0BD
398
1E4
10E
0DA
14D
20F
DCS
bits
11-0
925
934
935
936
943
946
94E
95A
966
975
986
98A
994
997
999
99A
9AC
9B2
9B4
9C3
9CA
9D3
9D9
9DA
9DC
9E3
9EC
DCS
DCS
DCS
Code
Code
Code
023
025
026
031
032
043
047
051
054
065
071
072
073
074
114
115
116
125
131
132
134
143
152
155
156
162
165
172
174
205
223
226
243
244
245
251
261
263
265
271
306
311
315
331
343
346
351
364
365
371
411
412
413
423
431
432
445
464
465
466
503
506
516
532
546
565
606
612
624
627
631
632
654
662
664
703
712
723
731
732
734
743
754
6B7
65D
51F
5F5
5B6
0FD
7CA
6F4
5D1
679
693
2E6
747
35E
72B
7C1
07B
3D3
339
2ED
37A
1EC
44D
4A7
6BC
31D
05F
1.5.3.4
Receiving and Decoding Selcall Tones
Selcall tones can be used to flag the start and end of a call. They may also occur during a call in which
case the tone may be audible at the receiver. If enabled, an interrupt will be issued when a signal
matching a valid Selcall tone is detected and when a present Selcall tone turns off or changes (i.e. at the
start and at the end of each Selcall tone). The audio path can then be turned on and off at the
appropriate times under control of the host µC.
The CMX881 implements a fully programmable Selcall encoder / decoder. The frequency of each tone is
defined in the Program registers P1.2-18. See section 1.6.20 for programming details.
In receive the CMX881 scans through the tone table sequentially, the code reported will be the first one
that matches the incoming frequency.
2004 CML Microsystems Plc
19
D/881/7
CMLMICRO [ CML MICROCIRCUITS ]
