CMX910 datasheet(49/61 Pages) CMLMICRO

49 / 61 page

AIS Baseband Processor

CMX910

D/910/6

5.11

C-BUS Expansion Port

The C-BUS expansion port facilitates the connection of the host µC to as many as six additional C-BUS

compatible devices, while only requiring one additional C-BUS chip select pin. To operate the expansion

port, the µC writes to the CBUS_Expand register through the CMX910’s normal C-BUS port (SCLK,

CDATA, CSN) – this can be done even when the CMX910’s internal clocks are disabled. Subsequently,

for each bit set in bits 5-0 of the CBUS_Expand register, taking the chip select expansion input (CSXN)

low will cause the associated EXP5N – EXP0N output pin to go low. Each of the EXP5N – EXP0N pins

can be connected to the (active low) chip-select input of another C-BUS compatible device. Usually only

one bit in the CBUS_Expand register would be set high at a time. Setting more than one bit high may

cause simultaneous selection of a number of C-BUS devices; in that case, care must be taken to avoid

contention if a common RDATA line is used.

If expansion of the C-BUS is not required, the outputs EXP5N – EXP0N can be used as general purpose

digital outputs by holding CSXN low and writing the required data pattern to the CBUS_Expand register.

The data will then appear on the EXP5N-EXP0N pins in inverted form.

CBUS_Expand register: 8-bit write only.

C-BUS Address $A0

All bits cleared to 0 on reset.

This register can be written while the CMX910’s internal clocks are disabled.

Bit:

Reserved,

set to 00

EXP5N

enab

EXP4N

enab

EXP3N

enab

EXP2N

enab

EXP1N

enab

EXP0N

enab

CBUS_Expand register b5-0: EXP5N – EXP0N Expansion Bus Enable

Each bit that is set to 1 causes the corresponding EXP5N – EXP0N output pin to be driven low

when the CSXN input pin is driven low. Bits that are set to 0 cause the corresponding EXP5N –

EXP0N output pin to be held high.

CMX910 Datasheet(PDF) 49 Page - CML Microcircuits