Buffered E.I. cable

[GK2001]

I've been trying in vain to find a schematic for one of these. If anyone can help I'd appreciate it.

 

[Eudimorphodon]

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]

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.

 

[GK2001]

I'm just curious as to how the data lines were buffered, if they were at all.

 

[Eudimorphodon]

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]

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]

This is an old schematic from Pascal Holdry who did a lot of amazing work in recreating the TRS-80 hardware.
> Charles