How to use the time in the 6530/6532

[Hans Otten]

When I acquired a KIM-1 Rev A, obviously sold by NCE/Compumart, it came with some documentation that may interest any programmer working with the MOS Technology (R)RIOT 6530 and 6532. The timer description the datasheet is a bit vague about how to use. What may help is the document 'KIM-1 Application Note 2 Interval Timer Operation' by MOS Technology. A document with listings of KIM-1 programs called 'KIM-1 Application Programs CT1' illustrate the usage of the timer in interrupt mode. You find the documents here:

Compumart KIM-1 Rev A – Retro Computing

[Eduardo Casino]

This is great!

I've been wanting to check for a while whether 6530 substitutes like mine, based on Ruud Baltissen's design, handle interrupts properly. I saw some time ago on the VCF forum that someone (I can't quite remember who) claimed they didn't, and that he had fixed it in his own design, which he didn't publish.

[Stefan S]

Only way to fix that is to patch the code or build a FPGA replacement.

There are rumors that there is at minimum one working FPGA replacement.

[Stefan S]

https://github.com/sajattack/yo6530

Mit freundlichen Grüßen

Stefan Szillat 

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Sent: Monday, August 11, 2025 2:01:36 PM
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Subject: Re: How to use the time in the 6530/6532

 

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[Eduardo Casino]

There is one, indeed:

https://github.com/sajattack/yo6530

But I'd also like to understand what the problem is with current designs. AFAIK, the VCF forum member claimed to have solved it with his.

[Hans Otten]

6530 hardware emulator in FPGA in 40 pin DIP – Retro Computing

It is real! I have them. And a recent update fixed a time issue!

GitHub - daglem/reDIP-RIOT: MOS 6530 RRIOT / MOS 6532 RIOT replacement

[Eduardo Casino]

Yup, that is the hardware, but Paul Sajna (sajattack) did the gateware!

[Stefan S]

Hans can you please describe the timing issues a bit further?

I know they are there but I got the impression they are minor and can be neglected in most of the cases.

As they result in minor timing deviations.

In simpler words the differences are measure able but not relevant in most applications.

I could be totally wrong as I do not know which software cares about that beside the alarm clock.

Best regards

Stefan

[Hans Otten]

I am not aware of timing issues besides in the GS65SC32 variant one clock tick off sometimes.
The 6530 timer is AFAIK identical to the 6532 timer.

The problem fixed in the FPGA by Paul Sajna was about interrupts not happening.

The times is used in the KIM-1 cassette routines to time the audio pulses. The monitor is relying on timed loops  for the TTY routines.
There are more examples, like the programs in the CT document this topic is about.