The module has the following features:

• Two PWM signal generators
• Single OUT instruction to set each PWM width
• Easily set from BASIC or other environment
• Tight address decoding
• Compatible with RCBus-Z80 (80-pin bus)
• Compatible with RC2014 systems

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

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, while a value of 128 sets the output signal at a steady high level. A value of 1 produces the most narrow pulse and 127 the most wide pulse.

The module provides a jumper to select from a range of clock rates and thus a range of pulse frequencies. A jumper is also provided to select the PWM clock source from the on board oscillator or a number of pins on the RCBus. Finally, there are jumpers to allow the output signals to be connected to a range of bus pins.

If the base I/O address is set to 6, then to set the value of the PWM pulse width you need to write the value to I/O address 6. PWM channel #2 width is set at I/O address 7.

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

• OUT 6, 100

To set the width of PWM channel #2 to 100 (decimal) in assembler:

• LD A, $64
• OUT (7), A

Documentation

The documentation can be found at www.smallcomputercentral.com

Compatibility

This module conforms to the RCBus specification v1.0 for RCBus-Z80 (80-pin bus) and RCBus-RC2014 (40 pin or 60 pin).

The RCBus specification includes RCBus-2014 (both RC2014 standard 40-pin bus and RC2014 enhanced 60-pin bus) and also the full 80-pin RCBus. The 80-pin RCBus provides support for advanced Z80 features, such as the interrupt daisy-chain, as well as support for other processor families.

The Kit

This kit includes all the components needed to make the module, as shown in the first picture. Other modules and backplanes shown in the pictures are not included. You will require tools, solder, and cleaning materials to assemble this kit.

Printed Circuit Board

The printed circuit board is available on its own here.

Complete Systems

If you are looking for a complete system the following products might be appropriate.

• SC126 RCBus-80pin Z180 RomWBW CP/M Motherboard
• SC720 RCBus-80pin Z80 RomWBW CP/M Motherboard
• SC791 RCBus-80pin Z80 RomWBW CP/M Computer
• SC792 RCBus-80pin Z180 RomWBW CP/M Computer
• SC114 RCBus-40pin Z80 SCM & BASIC Motherboard
• SC131 Pocket-sized Z180 RomWBW CP/M computer

Notes

• This product is supplied as a kit of parts that require assembly.
• It is your responsibility to pay any import duty or taxes charged by your home country.
• This product is designed for hobby use and is not suitable for industrial, commercial or safety-critical applications.