CMX882D6 View Datasheet(PDF) - CML Microsystems Plc
Part Name
Description
MFG CO.
'CMX882D6' PDF : 70 Pages View PDF
FRS Signalling Processor
CMX882
Table 9 Maximum Data Transfer Latency
Data encoding type
Max time to read from
or write to data buffer
1200b/s 2400b/s
Data buffer
size
0
13.3ms
6.6ms
2 bytes
1
N/A*
N/A*
4 bytes
2
13.3ms
6.6ms
2 bytes
3
20ms
10ms
2 bytes
4
40ms
20ms
4 bytes
5
40ms
20ms
4 bytes
* Type 1 message is an isolated Frame Head, there is no subsequent data to load (Tx) or read (Rx).
1.5.6 XTCSS Coding
The CMX882 allows addressed calling using a 4 tone In-band tone burst followed by an optional sub-
audio ‘XTCSS maintenance tone’ (at 64.7Hz). In transmit the CMX882 handles the transmission of the 4
tone sequence and the sub-audio tone. In receive the CMX882 will search for valid In-band tone
sequences containing the previously programmed address.
The over air signalling of XTCSS is shown below:
XTCSS sub-audio
In-band tones
Voice / Data
A
A1 A0 S0 S1
B
Notes:
• To reduce 'cut on' time with XTCSS voice calls, the host can enable the receive audio path at 'B'
(as soon as the 4 tone sequence is available), before the sub-audio is detected.
• XTCSS 4 tone sequences must be prefixed and suffixed with a silent 'no-tone' period of at least
the length of each tone. See also programming register P1.1.
In-band tones A1 and A0 are the BCD (binary coded decimal) representation of the Device Address bits
of $C2 register, the valid XTCSS address range is 01 to 99, A0 is the least significant digit. The XTCSS
address '40' is reserved for an all call address - regardless of the XTCSS address being searched for the
CMX882 will always indicate when a valid 4 tone set containing address '40' has been received.
In transmit the CMX882 will only generate the sub-audio maintenance tone when the CTCSS enable bit is
also set to '0'. The sub-audio tone (if enabled) will be automatically output after the 4th XTCSS tone has
been transmitted. An XTCSS interrupt is generated (if enabled) at point 'A' - see diagram above, the host
should then wait one tone period before enabling the audio path (or transmitting data) to ensure sufficient
no-tone suffix to the XTCSS 4 tone set. To summarize, detection of XTCSS sub-audio maintenance tone
requires the CTCSS decoder to be enabled, whereas generation of the XTCSS sub-audio maintenance
tone requires the CTCSS encoder to be disabled.
In-band tone S0 is selected from the normal tone range of $B - $D to maintain compatibility with HSC
type addressing. In-band tone S1 is selected from the normal tone range $0 - $9. The bit patterns for S0
and S1 indicate the type of information to follow according to the following tables:
2004 CML Microsystems Plc
32
D/882/7
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