Digital PMR Radio Processor
CMX7131/CMX7141
Table 14 C-BUS Data Registers
C-BUS Address
Function
C-BUS Address
Function
$B5
$B6
$B7
$CA
$CB
Tx data 0-7 and info
Tx data 8-23
Tx data 24-39
Tx data 40-55
Tx data 56-71
$B8
$B9
$BA
$BB
$C5
Rx data 0-7 and info
Rx data 8-23
Rx data 24-39
Rx data 40-55
Rx data 56-71
The Block ID is ignored in Raw Data mode, but should be set to 01 (payload) for consistency with NXDN
formatted mode (see User Manual section 8.1.17).
Bits 7 and 6 hold the Transaction Counter, which is incremented modulo 4 on every read/write of the Data
Block to allow detection of data underflow and overflow conditions. In Tx mode the host must increment
the counter on every write to the TxData block, and if the CMX7131/CMX7141 identifies that a block has
been written out of sequence, the Event bit (C-BUS register $C6, b14) will be asserted and an IRQ raised,
if enabled. The device detects that new data from the host is available by the change in the value of the
Transaction Counter, therefore the host should ensure that all the data is available in the TxData block
before updating this register (i.e. it should be the last register the host writes to in any block transfer). In Rx
mode, the CMX7131/CMX7141 will automatically increment the counter every time it writes to the RxData
block. If the host identifies that a block has been written out of sequence, then it is likely that a data
overrun condition has occurred and some data has been lost. If a CRC failure has been detected when
decoding the data block, an ‘Event’ IRQ is issued concurrently with the ‘Data Ready’ IRQ along with a
status code in the Modem Status register ($C9).
6.5.21 CMX994 Pass-through Mode
To allow the host to communicate directly with the CMX994 for test and configuration purposes, a pass-
through mode is available which allows any CMX994 C-BUS register to be written. This mode uses the
TxData0, RxData0 and Programming registers on the CMX7131/CMX7141.
To write to the CMX994:
o
o
o
o
o
Set the CMX7131/CMX7141 to CMX994 Pass-through mode ($C1=$0004)
Wait for the Program Flag to be set ($C6 b0)
Write the CMX994 data value to the TxData0 register ($B5)
Write the CMX994 C-BUS address to the Programming register ($C8) with b15-13=0112
Wait for the Program Flag to be set ($C6 b0).
2014 CML Microsystems Plc
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