• Please review our updated Terms and Rules here
  • Exhibitor application for VCF West 2022 is now open! If you are interested in exhibiting, please fill out the form here.

Buffered E.I. cable

GK2001

Experienced Member
Joined
Jul 17, 2017
Messages
147
I've been trying in vain to find a schematic for one of these. If anyone can help I'd appreciate it.

1652495114021.png
 

Eudimorphodon

Veteran Member
Joined
May 9, 2011
Messages
4,569
Location
Upper Triassic
I have one with a cracked open case that I’ve been meaning to probe out, I guess I should do that. It has been on my list to build a replacement PCB that has 32k SRAM chip and ties A15 low to override the EI memory because I’ve kinda lost patience with the whole DIN plug mess.
 

NeXT

Veteran Member
Joined
Oct 22, 2008
Messages
6,804
Location
Kamloops, BC, Canada
There's pictures floating of the NewBuff which was a replica of the buffered EI cable but it seems the site that lists it is currently down. I think the photos still work though.
s-l500.jpg
 

GK2001

Experienced Member
Joined
Jul 17, 2017
Messages
147
I'm just curious as to how the data lines were buffered, if they were at all.
 

Eudimorphodon

Veteran Member
Joined
May 9, 2011
Messages
4,569
Location
Upper Triassic
I just popped the lid off my original and did a little probing. Looks to me like, no, they're not, the D* signals pass straight through from one side to the other. Looks like the three '244s are entirely just addresses and control signals.
 

GK2001

Experienced Member
Joined
Jul 17, 2017
Messages
147
That's what I figured. If there was a bi-directional buffer such as a 74LS245 to handle the data lines, it would need an enable line derived from the address decoding inside the E.I. unit to prevent read contentions with the keyboard unit.
 

Dawsoca

Experienced Member
Joined
Jan 10, 2013
Messages
75
Location
Ft. Worth, Texas
This is an old schematic from Pascal Holdry who did a lot of amazing work in recreating the TRS-80 hardware.
> Charles
 

Attachments

  • copyright.txt
    893 bytes · Views: 8
  • Schema_Buffer_expansion_A.pdf
    11.7 KB · Views: 18
Top