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Plantronics colorplus 80 column character bottom cut off

S

snowman

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Mar 8, 2017
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Upper Peninsula of Michigan - U.S.
I found a plantronics colorplus. It had a missing character rom. I dropped a cga character rom in the socket (was told its compatible).
Problem: in 80 column character mode ONLY in color/16color mode the bottoms of the characters are cut off.
40 column with or without color is fine
ALL graphics modes are fine
16k ram tests fine in checkit
600x200 mode 80 column text is fine

Kind of baffled. I tried 2 cga roms same thing

As far as I can tell only 80 column text with color is affected

Feels like the crtc because of the cutoff?

See pics! :)
 

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What about 40 column text mode; are you absolutely sure that is okay? (Mode co40 in DOS.)

I think what it’s doing is displaying the top 8 lines of the 14 line tall MDA font. The ROM from an IBM CGA is shared with MDA and actually has three different fonts stored in it, maybe the Plantronics card is not using the correct offset.
 
Yes 100% certain 40col works fine. I forgot to supply pics.

I agree the offset could be incorrect. Anyone know how to only export the cga fonts from the cga rom? Looking at plantronics pictures online they use 4k 2732 roms so the rom is only 4k not 8k like cga.

Odd that only one video mode might be affected (color 80col mode).

Ill try and focus on nuying 2732 eproms to burn. If anyone knows the pieces of the cga rom Id need to dump that would definitively be helpful. I think each rom set is exactly 2k in the rom.
 
snowman said:
I agree the offset could be incorrect. Anyone know how to only export the cga fonts from the cga rom? Looking at plantronics pictures online they use 4k 2732 roms so the rom is only 4k not 8k like cga.
Click to expand...

Comparing the pinout on this page:


To that of a 2732 a notable difference is that the CGA ROM has A12 where A11 is. 4K is enough to hold two copies of the CGA character set (8 bytes per character X 256 characters = 2Kbytes), so… I wonder if Plantronics did something clever and designed their card so it’s supposed to flip A11 between 40 and 80 column mode (maybe they intended to have two slightly different fonts optimized for each mode?), but this is having the effect with the CGA ROM of instead making it display the top half of the MDA font *only* in 80 column mode.

Fonts in CGA graphics mode don’t come from the character generator on the card, they’re stored in the PC bios ROM, so those modes would work even with the CG completely absent.
 
… if you wanted to test this theory you could bend pin 21 on the CGA ROM so it doesn’t go in the socket and alternatively connect it via one of those little grabby probe wires to ground or +5v, preferably through a ~1K resistor.
 
Eudimorphodon said:
… if you wanted to test this theory you could bend pin 21 on the CGA ROM so it doesn’t go in the socket and alternatively connect it via one of those little grabby probe wires to ground or +5v, preferably through a ~1K resistor.
Click to expand...
Great idea. I think you are on to something. Meanwhile I investigated a 2732 adapter and found the 27512 is very near pin compatible for the 24pins that matter. I plan to make an adapter but will investigate testing with jumpers first. I have not found a plantronics rom dump yet... but I did find another thread where someone bit-shifted the cga rom until it lined up properly then burnt their own 2732. This thread is on vogons.
 
Thank you!!!! Yes I was struggling with the cga/mda font. I even built a tms27c512 adapter to 2732 and same issue heheh I cant wait to burn the file you posted when I get home. Cant say thanks enough!!!!
 
JohnElliott said:
Here's the Plantronics Colorplus ROM. It's a 4k ROM with the thin font in the first 2k and the thick font in the second 2k.
Click to expand...

I can’t remember off the top of my head if the MDA font is in the first or second half of the CGA ROM, do you recall? I ask because of this from your page:

“WJ4 / WJ5Font select: controls the A11 pin on the font ROM (or the A12 pin if it's a 9264). Putting the jumper on WJ4 will pull the line high (thick font); putting it on WJ5 will pull it low (thin font).”

With the pinout difference the state of this pin would control which half of the ROM is getting hit, which would mean MDA font or one of the CGA fonts; The card supposedly works in 40 column mode but isn’t 80 column, is it possible the jumper is missing from here, letting this line float? I can’t think of a good reason why it would consistently float one way or another between those two modes (floating inputs can be weird), but if we pretend this is a workable theory *and* the jumper is missing then maybe this can be fixed by just adding a jumper to hold it correctly.
 
The MDA / CGA ROM has the 8x14 font in the first half, and the two CGA fonts in the second half.

Regarding the jumpers, bear in mind that my card didn't appear to work, so anything I say about them comes from following the traces rather than being verified experimentally.

Plantronics card font ROM:
u26.png

MDA / CGA font ROM:
ibmmda.png
 
Success!!! Million thanks once more for uploading your plantronics character rom.

I took a pic of my jank 27c512 to 2732 adapter also. I need to ground the unused address pins still. I wanted to test quick before finishing the grounding.

I ordered proper 2732’s

Side note these plantronics cards only like a 4.77 mhz bus! If I hit the turbo 10mhz button the card wigs out with memory errors heheh. I wonder if swapping out the bus transceivers would fix that?
 

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So a thing I’m noticing here is in 80 column mode you’re getting the “thin” font. You did not include a screenshot of 40 column text mode, by any chance is it using the fat font? If it is then the situation you got with a CGA font is completely explained. (You could have made the CGA font rom work by tying pin 21 high.)
 
snowman said:
It definitely was using the fat font. I will test again (later today) to pull 21 up with a 1k resistor. Maybe my probe clips were not making good contact at one of the link points.
Click to expand...

Are you saying it’s WAS using the fat font for 40 column with the CGA ROM in it but it’s the thin font with the right ROM in there, or is it the fat font NOW?

Just curious, because if the Plantronics switches between thin/fat for 80/40 column that’s a factoid I’d never heard about it, and it simultaneously would explain what happens with the CGA rom in there.
 
When the cga rom was installed and pin 21 was grounded = fat font for 40col and messed up 80 col font

Cga rom installed w/ pin21 at 5v = thin 40col font. And proper thin 80 col font (Just tested) so the cga rom functions fine with pin 21 pulled to 5v. I must have had bad contact earlier.

Proper plantronics rom = thin font 40 col and thin font 80 col as expected

Sorry for the confusion hope that clarifies things.
 
snowman said:
Proper plantronics rom = thin font 40 col and thin font 80 col as expected
Click to expand...

Huh. Okay, so… weird. These results indicate that pin 21 from the card *should be* low all the time. (The thin font is the first one in the ROM, so A11 needs to be low to see it instead of the fat font.) When you put the CGA ROM in A11 on the ROM goes to an /OE line in the socket, which should always be low, so it makes sense you see the thin font when you’re holding 21 high with the jumper. (The CGA fonts are in the second half of the CGA ROM, so A12 needs to be high.)

The big mystery, then, is why in the world was pin 21 going low in 80 column (switching to the MDA font) but was high in 40 column. It seems like it *must* be a bad connection and for some reason (interference?) the pin was floating a different direction in different modes.
 
The 40-column screenshots in the initial post are of graphics mode, where the font comes from the BIOS and the on-card font ROM doesn't get involved. Unless I've missed something there aren't any screenshots of the 40-column text mode.
 
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