Telephone Signalling Transceiver / Least Cost Router
CMX860
1.5.12 'C-BUS' Interface
This block provides for the transfer of data and control or status information between the CMX860’s
internal registers and the µC over the 'C-BUS' serial bus. Each transaction consists of a single Register
Address byte sent from the µC which may be followed by one or more data byte(s) sent from the µC to be
written into one of the CMX860’s Write Only Registers, or one or more byte(s) of data read out from one
of the CMX860’s Read Only Registers, as illustrated in Figure 7.
Data sent from the µC on the Command Data line is clocked into the CMX860 on the rising edge of the
Serial Clock input. Reply Data sent from the CMX860 to the µC is valid when the Serial Clock is high.
The CSN line must be held low during a data transfer and kept high between transfers. The 'C-BUS'
interface is compatible with most common µC serial interfaces and may also be easily implemented with
general purpose µC I/O pins controlled by a simple software routine. Figure 13 gives detailed 'C-BUS'
timing requirements.
The following 'C-BUS' addresses and registers are used by the CMX860:
General Reset Command (address only, no data).
General Control Register, 16-bit write only.
Transmit Mode Register, 16-bit write-only.
Receive Mode Register, 16-bit write-only.
Transmit Data Register, 8-bit write only.
Receive Data Register, 8-bit read-only.
Status Register, 16-bit read-only.
Address $01
Address $E0
Address $E1
Address $E2
Address $E3
Address $E5
Address $E6
Programming Register, 16-bit write-only.
Analogue Signal Path Register, 8-bit write-only.
Address $E8
Address $EC
Notes: 1. The 'C-BUS' addresses $E9, $EA and $EB are allocated for production testing and should not
be accessed in normal operation.
2. The 'C-BUS' address $E4 is allocated for internal use and should not be accessed in normal
operation.
3. In several registers there are bit patterns whose function is not specified. These modes
should not be accessed in normal operation and no guarantee is given that any use of these
bits will be supported in the future.
1.5.12.1
General Reset Command
(no data)
General Reset Command
'C-BUS' address $01
This command resets the device and clears all bits of the General Control, Analogue Signal Path,
Programming, Transmit Mode and Receive Mode Registers and all bits of the Status Register except b14
and b8.
The clearing of the General Control Register will put the device into Powersave. See the description of
General Control Register b8 for the procedure on how to power-up the device.
Whenever power is applied to the CMX860 a General Reset command should be sent to the device, after
which the General Control Register should be set as required.
ã 2002 Consumer Microcircuits Limited
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