FRS Signalling Processor
CMX882
B as required. The only task the host need perform during the reception of formatted Frames is to read
out data when it is ready.
Note: These 2 words must be read separately. i.e. Two 16 bit C-BUS transactions.
1.6.19
$CC TONES STATUS: 16-bit read-only
15
14
13
12
11
10
9
8
7
0
6
0
5
4
3
2
1
0
Bit:
Detected Selcall tone frequency
Sub-Audio Status
Detected CTCSS code
This word holds the current status of the CMX882 sub-audio and In-band tone sections. This word should
be read by the host after an interrupt caused by a DCS, CTCSS or In-band tone event.
The value in bits 5 to 0, Detected CTCSS code, identifies the detected sub-audio tone by its position in
Table 3 CTCSS Tones. If bits 5 to 0 = '000000' there is no CTCSS tone currently being detected. If bits
5 to 0 = '110111' (= 55 in decimal) this indicates that an Invalid Tone has been detected. An Invalid Tone
is any tone in the subaudio band which is not the selected subaudio tone nor the all-call tone, or is a tone
not listed in Table 3. A change in the state of bits 5-0 to Invalid Tone from the no tone condition will not
cause Status register ($C6), b11 to be set to '1'. Any other change in the state of bits 5-0 will cause the
Status register ($C6), b11 to be set to '1'.
A detected In-band frequency is indicated by the value in bits 15 to 11, ‘Detected In-band tone
frequency’, identifies the frequency by its position in Table 6 In-band Tones. If bits 15 to 11 = '00000'
there is no In-band tone currently being detected. A change in the state of bits 15 to 11 will cause bit 13
of the Status register ($C6), ‘In-band State Change’, to be set to '1'.
Bits 10 to 8 indicate the DCS and special sub-audio tone status. The Status register ($C6) will indicate
the type of signal detected. If DCS or special CTCSS tones are detected they will be indicated in bits 10
to 8 according to the table below and bits 7 to 0 will be set to '00000000'. If a normal CTCSS tone is
detected bits 10 to 8 will be set to '000' and bits 7 to 0 will indicate the decoded tone. A change in the
state of bits 10 to 8 will cause the relevant bit (10 or 11) of the Status register to be set to '1'.
Bit 10 Bit 9 Bit 8
Sub-Audio status
0
0
0
0
1
1
1
1
0
0
1
1
0
0
1
1
0
1
0
1
0
1
0
1
No DCS or special CTCSS detected
Reserved
DCS sequence detected
inverted DCS sequence detected
Reserved
Only enabled with DCS
Only enabled with DCS
134.4Hz DCS turn off tone detected
64.7Hz XTCSS sub-audio tone detected
Reserved
Only enabled with DCS
Only enabled with XTCSS
When the relevant detection mode is not enabled, the associated bits will be set to '0'. In Tx mode this
register will be set to '0'.
During DCS receive, the device can flag an interrupt when the DCS code fails to be recognised. This may
be due to code dropout. The turn off tone may be flagged shortly after, if the transmission is ending.
Alternatively the DCS link may be restored and DCS detection will be flagged again.
2004 CML Microsystems Plc
49
D/882/7
CMLMICRO [ CML MICROCIRCUITS ]
