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80-column video options for RC2014 15KHz [message #8217]

Thu, 21 January 2021 12:06

quarterturn
Messages: 86
Registered: April 2018

Member

Any 80-column 15 KHz video options known for the RC2014 Z80 standard? I have a few RC2014 systems, as well as a collection of 15 KHz amber and green displays, and I'd like to re-create the experience of running something like what the Tandy Model 4 offered with the high-res video option - 640x240 bitmapped graphics.

ROMWBW supports TMS9918, SY6545, MOS8563, HD6445, and out of those I think MS8563 and SY6545 would be appropriate for 80-column. Plasmo has a VGA card using EPM7128S which in theory shouldn't be difficult to mod for 15 KHz, though I'd have to inquire as to if he's got any console support for it. Bonus if it can be designed to fit on the enhanced RC2014 protoboard from dtronixs. I'm also aware of the 15 KHz card for the ECB standard. I'm not opposed to using a CPLD or FPGA, though at the moment I lack the skills to implement that myself.

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Re: 80-column video options for RC2014 15KHz [message #8218 is a reply to message #8217]

Thu, 21 January 2021 17:41

plasmo
Messages: 916
Registered: March 2017
Location: New Mexico, USA

Senior Member

Interesting question and timely as well. I'm gathering up hardware to see if I can port Tandy Model 4 TRSDOS (aka LS-DOS) to RC2014 environment. The ultimate target is a SBC similar to Z80ALL, but the pathfinder hardware is 2 boards, Z80LCD for Z80/memory/CFdisk and VGARC for video and keyboard.
https://www.retrobrewcomputers.org/doku.php?id=builderpages: plasmo:z80lcd
https://www.retrobrewcomputers.org/doku.php?id=builderpages: plasmo:vgarc

Both boards have under-utilized CPLD so that should give me the extra logic needed for experimentation.

There are many things I don't know about Tandy graphic. Since VGARC can do 640x480 at 31.5KHz, it should be possible to slow it down to 15KHz and 640x240. But can Model 4 really do bit map at 640x240? that requires at least 20K byte of graphic memory. I don't recall Model 4 has that much graphic memory. I can see 80x24 text-only display for 640x240, which VGARC definitely can do. Obviously I need to do more research.

Bill

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Re: 80-column video options for RC2014 15KHz [message #8219 is a reply to message #8218]

Thu, 21 January 2021 18:29

lowen
Messages: 226
Registered: August 2016
Location: Western NC USA

Senior Member

Hey, plasmo,

The Model 4 has an I/O mapped hires option board that had 32K of RAM for a full 640x240 display, with some room for horizontal and vertical scrolling. The Model 4P Service Manual has information on it. I'll look up the page references when I'm back in front of my laptop.

EDIT: pages 189-195 (PDF pages 191-197). The 32K of RAM is implemented as 64Kx4 bits.

--
Bughlt: Sckmud
Shut her down Scotty, she's sucking mud again!

[Updated on: Thu, 21 January 2021 18:39]

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Re: 80-column video options for RC2014 15KH [message #8220 is a reply to message #8219]

Thu, 21 January 2021 19:07

quarterturn
Messages: 86
Registered: April 2018

Member

There was a cheaper third-party option as well which had the minimum 19K RAM. I have an original CGA card somwhere which could donate its CRTC, but I wouldn't use it in a kit due to supply challenges like counterfeiting. CPLD seems like the way to go.

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Re: 80-column video options for RC2014 15KH [message #8221 is a reply to message #8220]

Thu, 21 January 2021 21:00

lowen
Messages: 226
Registered: August 2016
Location: Western NC USA

Senior Member

Yes, the Microlabs Grafyx Solution; thanks for the reminder. Ian Mavric in Australia has replicas of the Grafyx Solution available. The nice thing about the Microlabs board is that it's all simple TTL chips, other than the RAM.

I totally agree about CPLD; reliable noncounterfeit sourcing of in-demand CRTC's like 6545 is getting increasingly difficult.

--
Bughlt: Sckmud
Shut her down Scotty, she's sucking mud again!

[Updated on: Thu, 21 January 2021 21:03]

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Re: 80-column video options for RC2014 15KH [message #8223 is a reply to message #8221]

Fri, 22 January 2021 10:19

quarterturn
Messages: 86
Registered: April 2018

Member

This showed up on tindie pretty recently: https://www.tindie.com/products/dinotron/v9958-msx-video-boa rd-for-rc2014/

V9958 can do 512x212 which is just enough for 80x24. Not really a cheap option, though. Also needs a keyboard option for true standalone operation.

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