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GENDON3 improved character generator for the Model I Discussion

@Larry

There's another mod done to the motherboard which allows the extra row of character generator dots to be visible. Read the installation instructions carefully - difficult, as the scan is from a pretty faded original.

I'll have a bit of a look later and try to explain it.

Ian.
 
In an ordinary TRS-80, only three video line addressing bits (L1, L2, and L4) are sent to the character generator, and therefore only 8 lines can be generated per character. The fourth signal, L8, is instead sent as an input (Z26.12, after a delay through Z27) to the AND gate controlling the enable of the character-pixels shift register (Z10). This is what prevents the top four lines of the character being repeated in the bottom four lines of the 12-line character cell (and instead causes those four lines to be blank).

When the Gendon mod is done, L8 is removed from the shift-register's enable AND gate, and is instead sent to the EPROM to be used as a fourth video line address bit (A3 of the EPROM, pin 5). That allows the EPROM to generate 16 distinct lines per character (and it requires each character in the ROM to be 16 bytes away from neighboring characters), but the line addresses get reset to zero after 12 lines, so only 12 lines of data are ever used.

The other change is that an extra (sixth) bit is output from the EPROM (Q5, pin 15) and sent to the first-out bit on the shift register (Z10.14), which is normally connected to ground (and therefore normally causing the leftmost column of every character to be blank).

Together, those changes increase the ROM-controlled area of the character cell from 5x8 to the full 6x12 dimensions of the cell.
 
Ian/Petrofsky,
I was totally unaware of those video mods for the Model 1. That sure is an interesting modification.

THANKS.

Larry
 
Ian,
For the Photo of the GenDon3 EPROM Adapter I have the following connections:

CG------PIN-----PIN-----EPROM 2716

RS1-----11 A0--- 8------A0
RS2-----10 A1----7------A1
RS3----- 8 A2----6------A2
-----------------5------A3 Purple Wire is Row L8 from Z12 Pin 11 (L8 Added to Character Rows L1, L2, L4)
A0------ 7 A3----4------A4
A1------ 6 A4----3------A5
A2------ 5 A5----2------A6
A3------ 4 A6----1------A7
A4------ 3 A7---23------A8
A5------ 2 A8---22------A9
A6------ 1 A9---19------A10
D0------12 D0----9------D0
D1------13 D1---10------D1
D2------14 D2---11------D2
D3------15 D3---13------D3
D4------16 D4---14------D4
GND------9 --------------- NO CONNECTION
CS------17 CS---20------OE
----------------18------CE (Jumpered to VSS of EPROM)
----------------12------GND (ONLY have GND to EPROM when CS present)

VCC-----18------24------VCC
----------------21------VPP (jumpered to VCC of EPROM)

----------------15------D5 Grey Wire to Z10 Pin 14 is 6th bit of Character Cell (Bit5 is always a blank cell)
----------------16------D6 -- From EPROM - NOT USED
----------------17------D7 -- From EPROM - NOT USED

I an wondering why Don didn't connect the GND (Pin 9) of the Character Generator Socket on the Adapter to Pin 12 of the EPROM,
versus using a Jumper from the EPROM's Socket EPROM Pin 18 to EPROM Pin 12?

I wouldn't think a floating GND on an EPROM, when it's not selected would be a good thing.


Did you ever get a good READ of the 2716 EPROM? I'd Like a copy of the HEX BYTES. Will you Please post it?


Thanks.

Larry
 
Ian,
The "PCB" for the GENDON3 I did works? And the 512K memory extension for COCO?
I have to finish a Video Genie printer interface adapter to BUS EXPANSION TRS-80 M1.
A+
Pascal

Le "PCB" pour le GENDON3 que j'ai fait fonctionne? et l'extension mémoire de 512K pour le COCO?
Je dois bientôt terminer un adaptateur interface imprimante Vidéo Génie vers BUS EXPANSION TRS-80 M1
 
Ian, I have been unable to connect to your site since you first published the new addy. Every attempt results in: Error Code: INET_E_RESOURCE_NOT_FOUND

Mike
 
TRS-Ian said:
Instructions complete thanks to John G. in NZ. Have a read and let me know what you think?

http://members.iinet.net.au/~ianmav/downloads/GenDon%203%20Character%20modification%20installation%20for%20the%20TRS80%20Model%20I.zip

Cheers,

Ian.
Click to expand...

I gather your site has relocated to iinet? Hadn't seen an official announcement.

PS - only one comment on the instructions - Your first point is "Two track cuts are required . . . " then you go on to describe three cuts (Z10/14->Z11/3, Z10/14, Z27->Z26/12)

PJH
 
Well spotted PJH, i had to read it a couple of times myself (it was written by John G.) and I think what he's saying is there are two trace cuts on the component side of the motherboard, then another one on the solder-side. I'll update the doc when I get a chance.

@Avia, @Mike, there might be teething problems with the web site's new home, though I have been unable to reproduce the error you are getting here. Can you advise if you can get to any of these web pages which are just linked to from the main one:

http://members.iinet.net.au/~ianmav/trs80/model4s.htm

http://members.iinet.net.au/~ianmav/trs80/newstuff.htm

http://members.iinet.net.au/~ianmav/trs80/emulator.htm

http://members.iinet.net.au/~ianmav/trs80/downloads.htm

http://members.iinet.net.au/~ianmav/hires/hires.htm

http://members.iinet.net.au/~ianmav/Hans/

http://members.iinet.net.au/~ianmav/trs80/clearlysuperior.htm

I might have to make a new simplified homepage to facilitate people from other countries easily accessing the site.

Cheers,

Ian.
 
Same issues with those links Ian. The browser takes some time attempting to access the pages, but times out (IE + Firefox)

This page can’t be displayed

•Make sure the web address http://members.iinet.net.au is correct.
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