V23 / Bell 202 Modem
CMX624
1.5.11 ‘C-BUS’ Interface
This block provides for the transfer of data and control or status information between the CMX624’s
internal registers and the µC over the ‘C-BUS’ serial bus. Each transaction, see Figure 7, consists of a
single Register Address byte sent from the µC which may be followed by a single data byte sent from the
µC to be written into one of the CMX624’s Write Only Registers, or a single byte of data read out from one
of the CMX624’s Read Only Registers, as illustrated in Figure 7.
Data sent from the µC on the Command Data line is clocked into the CMX624 on the rising edge of the
Serial Clock input. Reply Data sent from the CMX624 to the µC is valid when the Serial Clock is high. The
interface is compatible with the most common µC serial interfaces such as SCI, SPI and Microwire, and
may also be easily implemented with general purpose µC I/O pins controlled by a simple software routine.
See Figure 10 for detailed ‘C-BUS’ timing requirements.
Figure 7 ‘C-BUS’ Transactions
2003 CML Microsystems Plc
13
D/624/7
CMLMICRO [ CML MICROCIRCUITS ]
