New hardware I/O board using Parallax Propeller

Any discussions related to the creation of new hardware or software for the ZX80 or ZX81
tdg8934
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Re: New hardware I/O board using Parallax Propeller

Post by tdg8934 » Thu Jun 13, 2019 9:45 am

Thanks Bean. Yes I have had many propeller cards over the years. I just haven’t played with one in a couple of years. I’m pretty familiar with Spin but only mildly familiar with Propeller ASM.

Bean
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Joined: Fri Aug 01, 2014 8:40 pm

Re: New hardware I/O board using Parallax Propeller

Post by Bean » Thu Jun 13, 2019 1:48 pm

I've decided to put the 16K of RAM on my board also.
Can someone explain what I have to do so that it support true Hi-Res mode ?
And maybe why it needs to be done ?

Thanks,
Bean

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1024MAK
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Location: Looking forward to summer in Somerset, UK...

Re: New hardware I/O board using Parallax Propeller

Post by 1024MAK » Fri Jun 14, 2019 12:26 pm

Wilf goes into considerable detail about the ZX81 video system here ;-)

Yes, we know that the pages are full of ? symbols (discussed on here a while ago).

In order for RAM to be hi-res capable, it must output data during both the Z80 read cycle and during the Z80 refresh cycle. So when either /RD is low or when /RFSH is low.

Does that help?

Mark

Bean
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Re: New hardware I/O board using Parallax Propeller

Post by Bean » Sun Jun 16, 2019 4:59 pm

Does this look correct for 16K that is True Hi-Res compatible ?

P.S. I forgot to show that /RAMCS is tied high too.

Thanks,
Bean
Attachments
16K HiRes.png
Last edited by Bean on Mon Jun 17, 2019 2:10 pm, edited 1 time in total.

tdg8934
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Re: New hardware I/O board using Parallax Propeller

Post by tdg8934 » Mon Jun 17, 2019 1:27 pm

Bean,

I like how you did 16K with only 2 chips. However, have you seen Wilf's circuit for 64K (2 - 16K RAMs) which says it's compatible with all Hi-Resolution formats?

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

I had one of my TS1000's modified at some point back to 32K using a 62256 but now I use the 32K memory built in on my ZXPand+.

You're project sure looks interesting!

Tim

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