This is a simple 8-bit PWM generator that is compatible with 8bit microprocessor buses.

Pulse frequency is 1/256 the clock frequency.

Very little overhead is required for it's use in terms of code or CPU usage. You just need to write a single byte to it whenever you need to change the pulse width. Works like a charm.

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Bill

Looks good, Bill. And it's nice that your machine has slots that can very readily accommodate an accessory like this.

As a timebase it uses the bus clock, is that right? The logic you're using has a lot of headroom, speed-wise. If someone wanted to use a higher clock frequency it'd be very easy to switch to using a can oscillator as a timebase.

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In 1988 my 65C02 got six new registers and 44 new full-speed instructions!
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Thanks.

Yes, that is the case in my implementation. It suits my needs right now, but I can envision wanting to design one with a programmable clock. My use so far has been with a 1.8432MHz version of my system - so the pulse frequency is 7.2KHz.

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Bill

Nice.
You may use /RCO and /P=Q as pulse outputs additionally. /RCO is "0" when the counter = $FF. /P=Q would always precede P>Q by one clock. Perhaps useful as a trigger?

Yeah, you could put a 74LS74 in there and have nice divide by 512 and 1024 square waves for ... whatever you'd need them for.

Using a 74AS885 would offer some advantages over the 74LS682, not the least of which is a simpler layout.

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Bill