Sinclair ZX80 / ZX81 / Z88 Forums

I want to do some testing on my TS 1000, I would want to remove the resonator and put in a small PCB with a switch (on/in & Off out ) to another source pin for another clock. say slower than slow.

Has someone done this yet? is just that simple?

Your thoughts?
Thanks

Keep in mind that any change to the main oscillator frequency will kill the video display, as the ULA and CPU timing comes from this main oscillator. It is the combination of the CPU and ULA working together that generates the video display.

The other problem, is that the ULA main oscillator pin is kind of, both an input and an output...

Mark

Mark,

Thanks. I did suspect slowdown could affect the display, as that is what "slow" does.
The ula interaction with the clock ... I did not know of .
But someone did say the ula runs the video framing. SO if that is going on,
it must be "using the clock" to keep it all in sync.

My Issue 3 TS1000 has a socketed Z80. It will be easier to pull it and put it on the breadboard.

I Know that the z80 is running and the ula is putting out the video signal.

I was wanting to slow it down enough to read some LEDs or hook up my Arduino to the data lines.

still thinking...

What about an input / output bit mapped memory circuit?

http://www.user.dccnet.com/wrigter/inde ... XRAMIO.htm

Use PAUSE and delay loops to control timing of lights ( need transistors for driving LED ) and read/write data...

vwbz80a wrote: ↑Mon Dec 11, 2017 4:14 pm I did suspect slowdown could affect the display, as that is what "slow" does.
The ula interaction with the clock ... I did not know of .
But someone did say the ula runs the video framing. SO if that is going on,
it must be "using the clock" to keep it all in sync.

Both the Z80 AND the ULA are responsible to generate a valid picture on TV. Thus both must be running on "normal" speed (a "realtime task").
For details see:
http://www.user.dccnet.com/wrigter/inde ... torial.htm

If you want to run the Z80 during normal program execution (NOT during display) with lower (or higher) clock rate, you need to install something like Wilf's "clock doubler" circuit to get e.g. "half" the normal speed:

http://www.user.dccnet.com/wrigter/inde ... /turbo.htm

Regards
Siggi

Siggi,
Thanks for the info on the video timing. Very helpful information!

Gammaray,
Thanks for the info also.

The link Is interesting! But probably over my head.
The idea of using bit mapped out put , is a possible path to a solution.. thought.
And along that line....... I do have a z80 PIO chip that could be put on the back buss connecter. Thinking that over.