Need a clue on a Z80 wait-state generator. - UK Vintage Radio Repair and Restoration Discussion Forum

acollins22 · 30th Aug 2020, 12:43 pm

Hi Folks,

I'm going back to one of my old Z80 machines and tinkering with a cf card reader. I would like to introduce a wait-state or two when reading it as I suspect timing is at the bottom of a problem I am having.

In fact, a wait state on any I/O read would be fine.

I have looked around the web for clues but I haven't found what I'm after and don't quite know enough to spin my own.

Does anyone out there know of a suitable snippet of a schematic they could point me at please?

Thanks,

Andy.

30th Aug 2020, 4:03 pm

I am rather surprised that a Z80 needs wait states for a CF card, those cards are quite fast. If needed why not reduce the clock frequency?

Mark1960 · 30th Aug 2020, 6:20 pm

You could try the example for adding wait states to M1 cycles from the mostek z80 technical manual. Page 69. But use /Iorq instead of /M1.
http://nascomhomepage.com/pdf/z80-mostek.pdf

The above will stop working correctly as the clock frequency is increased due to setup time on /WAIT input, but should be ok up to 10-14MHz.

Its unlikely to be a solution to the problem with the compact flash.

I would suggest taking a look at the retro-comp google group, recent thread on CP/M unstable on SC114, but many other threads with a similar solution posted by Bill Shen and verified by many others.
https://groups.google.com/g/retro-comp/c/p02uSv8olyU

RC2014-Z80 might also be worth looking at for z80 info.

Mark

acollins22 · 30th Aug 2020, 9:46 pm

Thank you Mark,

I didn't think to RTFM! I'll try that.

You may well be right about the wait states and CF cards but someone who knows this stuff better than me suggested I give it a try, so I will*.

Cheers,

Andy.

*This doesn't apply to everything people tell me to do. I wouldn't have reached this ripe age if I'd done that!

Slothie · 5th Sep 2020, 4:21 pm

Look at Grant Searle's CP/M on a breadboard computer, he uses a Compact Flash card as disk drive.

http://www.searle.wales/

30th Aug 2020, 12:43 pm	#1
acollins22 Pentode Join Date: Oct 2010 Location: Melton Mowbray, Leicestershire, UK. Posts: 156	Need a clue on a Z80 wait-state generator. Hi Folks, I'm going back to one of my old Z80 machines and tinkering with a cf card reader. I would like to introduce a wait-state or two when reading it as I suspect timing is at the bottom of a problem I am having. In fact, a wait state on any I/O read would be fine. I have looked around the web for clues but I haven't found what I'm after and don't quite know enough to spin my own. Does anyone out there know of a suitable snippet of a schematic they could point me at please? Thanks, Andy. Last edited by acollins22; 30th Aug 2020 at 1:12 pm.

30th Aug 2020, 4:03 pm	#2
Guest Guest Posts: n/a	Re: Need a clue on a Z80 wait-state generator. I am rather surprised that a Z80 needs wait states for a CF card, those cards are quite fast. If needed why not reduce the clock frequency?

30th Aug 2020, 6:20 pm	#3
Mark1960 Octode Join Date: Mar 2020 Location: Kitchener, Ontario, Canada Posts: 1,294	Re: Need a clue on a Z80 wait-state generator. You could try the example for adding wait states to M1 cycles from the mostek z80 technical manual. Page 69. But use /Iorq instead of /M1. http://nascomhomepage.com/pdf/z80-mostek.pdf The above will stop working correctly as the clock frequency is increased due to setup time on /WAIT input, but should be ok up to 10-14MHz. Its unlikely to be a solution to the problem with the compact flash. I would suggest taking a look at the retro-comp google group, recent thread on CP/M unstable on SC114, but many other threads with a similar solution posted by Bill Shen and verified by many others. https://groups.google.com/g/retro-comp/c/p02uSv8olyU RC2014-Z80 might also be worth looking at for z80 info. Mark

30th Aug 2020, 9:46 pm	#4
acollins22 Pentode Join Date: Oct 2010 Location: Melton Mowbray, Leicestershire, UK. Posts: 156	Re: Need a clue on a Z80 wait-state generator. Thank you Mark, I didn't think to RTFM! I'll try that. You may well be right about the wait states and CF cards but someone who knows this stuff better than me suggested I give it a try, so I will. Cheers, Andy. This doesn't apply to everything people tell me to do. I wouldn't have reached this ripe age if I'd done that!

5th Sep 2020, 4:21 pm	#5
Slothie Octode Join Date: Apr 2018 Location: Newbury, Berkshire, UK. Posts: 1,287	Re: Need a clue on a Z80 wait-state generator. Look at Grant Searle's CP/M on a breadboard computer, he uses a Compact Flash card as disk drive. http://www.searle.wales/