• Please review our updated Terms and Rules here

Simple, generic 80x24(25) display card

... For the VGA mod, are you referring to the instructions here? I'm looking at them and... gotta be honest, I'm thinking that most LCD VGA displays are *not* going to like the signals coming out of this.

This mod is literally just double-clocking the entire timebase used by the CRTC controller in it, effectively just throwing out NTSC framing twice as fast, IE, 120 262-line non-interlaced frames a second instead of 60; VGA is 60 525-line noninterlaced frames per second. I can see how this could trick a CRT VGA display into working because the *lines per second* count is the same as VGA and it's hsync rate that usually sets the lower limit for what a multisync CRT will accept, everything else is negotiable, but LCD scalers... I'm going to guess your mileage is going to vary a lot with this one.

The proper way to turn this into a VGA capable card would be to not just double-clock it, but modify the CRT controller programming to actually spit out appropriate framing. The source for the driver is in the manual and the controller can do enough scanlines, so not a huge deal, but a knock-on effect is you’ll want to change the character generator circuit to use more scanlines.
 
Eudimorphodon said:
... For the VGA mod, are you referring to the instructions here? I'm looking at them and... gotta be honest, I'm thinking that most LCD VGA displays are *not* going to like the signals coming out of this.

This mod is literally just double-clocking the entire timebase used by the CRTC controller in it, effectively just throwing out NTSC framing twice as fast, IE, 120 262-line non-interlaced frames a second instead of 60; VGA is 60 525-line noninterlaced frames per second. I can see how this could trick a CRT VGA display into working because the *lines per second* count is the same as VGA and it's hsync rate that usually sets the lower limit for what a multisync CRT will accept, everything else is negotiable, but LCD scalers... I'm going to guess your mileage is going to vary a lot with this one.

The proper way to turn this into a VGA capable card would be to not just double-clock it, but modify the CRT controller programming to actually spit out appropriate framing. The source for the driver is in the manual and the controller can do enough scanlines, so not a huge deal, but a knock-on effect is you’ll want to change the character generator circuit to use more scanlines.
Click to expand...
The one discussed at S100computers.com - http://www.s100computers.com/Hardware Folder/SD Systems/8024 VDB/SD Systems 8024 VDB.htm. I'd probably not do it because just changing the clock and a few chip types seems a bit 'odd'..... But then again, given how easy the mod is in that document, it might be worth a try just for giggles.
 
MykeLawson said:
The one discussed at S100computers.com - http://www.s100computers.com/Hardware Folder/SD Systems/8024 VDB/SD Systems 8024 VDB.htm.
Click to expand...

Yes, that's what I linked to.

Like I said, I'd be *really* surprised if that worked on a modern LCD monitor. (Or even a pretty old one.) I think the only reason it "works" on CRT multisyncs is the resulting output is essentially treated as if it were interlaced. (IE, it's interpreting those 120 262 line frames into 120 "fields" for 60 interlaced frames, even though the framing isn't really right.) Interlaced support is vanishingly rare on LCD scalers.
 
Anyway. Back to the origin of this thread, I guess the only thing I'd say about that card is it's not really a "simple" display card (per the subject line), it's essentially all the guts of a stand-alone terminal on a card; the only difference is it's skipping the serial UART and presenting a parallel interface instead.

... Which, you know, if that's the project you want, go for it. It's a pretty clean design with a relatively low parts count for a terminal of that vintage. Just noting that functionally it's not going to behave like a "video card"; the main CPU in the system has no direct access to VRAM and you're not going to be able to play with porting early video games or whatever to it.

(Which, I guess considering you were talking about eliminating direct memory mapping on the Flashwriter, isn't really what you were looking for anyway.)
 
Hi,

I have a "XITEX Dallas SCT-100 Composite Video with the Original Manual" I'd like to trade for some other S-100 boards. The White/Gold ceramic CPU is worth at least $1,000 ...

What have you to trade?


Boards I am looking for:
Processor Technology VDM-1
Morrow Thinker toys Disk Jockey II
ExpandoRAM 64K board
WameCo EPM-1 EEPROM board
Sol-20 System/Buss Probe board
MITS Altair 88-MU1 Systhesizer Board
Original DAZZLER board set
Cromemco Joy Stick(s)


.
 

Attachments

  • XITEX Dallas SCT-100-Front-Lc2KRc.jpg
    XITEX Dallas SCT-100-Front-Lc2KRc.jpg
    412.1 KB · Views: 5
wperko said:
The White/Gold ceramic CPU is worth at least $1,000 ...
Click to expand...

Really? Why? Because it's white ceramic?

The MK3870 on that board is a mask programmed microcontroller, it's useless for anything but what it's doing in this terminal. It's *mildly* interesting historically because it's based on the Fairchild F8 microarchitecture, but that's about it. I mean, maybe I'm off base thinking this but this doesn't seem likely to fetch as much as an 8080 or 6502.

If you want a white ceramic CPU there's a guy on eBay selling new-old-stock white ceramic Fujitsu clones of the Motorola 6802 for $20. That's a CPU you could actually build something with. (Bus-wise it's pretty much the same as 6502, you could use it to power a homebrew terminal no problem.)

For that matter there's are several BINs for white ceramic 8080s with 1976 date codes for $180-$200, and plenty of other examples of less well known gold/ceramic chips selling for under a hundred bucks. Selling prices north of a thousand seem to be pretty exclusively "@@LOOK: RARE EARLY MOS 6502 APPLE 1! TESTED!!!!" auctions.
 
Last edited:
And that is the beauty of wire-wrapping. I can build one, and if I don't like it, un-wire it and build the other one. And since the VDB-8024 has the driver code and the character generator code listed in the manual, I have far more control over what I can make it do. I will say I am moving in the direction of building that one first. Time will tell; after I get the basic machine built and functional to be at least equal the the STD based CP/M machine I have working now.
 
You must log in or register to reply here.
Back
Top