SC731 v1.2 PWM module for RCBus

SC731 is a two channel Pulse Width Modulation signal generator. It has tight address decoding and easy access with a single OUT instruction to set each PWM output.

The address decoding is such that one module takes only two I/O addresses (one for each PWM channel). Only writes to those addresses are decoded, so those addresses could be allocated to another device that only has a read function. Many of these modules can be installed in a single system as long as there are no address conflicts.

The output of each channel is set by writing a value from 0 to 128 decimal to the port address of the PWM channel. A value of zero turns the pulses off, leaving the output signal at a steady low level. A value of 128 turns the output constantly on with the output signal at a steady high level. A value of 1 produces the most narrow pulse and 127 the most wide pulse.

The frequency of the pulses is determined by the Clock frequency set with JP2. The frequency of the pulses is Clock/128.

Examples

If the base I/O address is set to 4, then to set the value of the PWM #1 pulse width you need to write the value to I/O address 4. PWM #2 width is set at I/O address 5.

To set the width of PWM #1 channel to 100 (decimal) in BASIC:
OUT 4, 100

To set the width of PWM #1 channel to 100 (decimal) in assembler:
LD A, $64
OUT (4), A