TRS-80 curiosity

Fred Cisin cisin at
Fri Apr 14 12:45:23 CDT 2017

On Fri, 14 Apr 2017, Bill Gunshannon via cctalk wrote:
> Well, I don'c consider something passive (having only inert parts) to be
> similar to a device with active parts, but that's just my opinion.  :-)

dissimilar designs can be done for functionally compatible systems.

> Mine is 40 pin to 50 pin, definitely for the Model I and looks exactly like the
> Screen Printer cable in the last picture I was sent.

Great!    Curiousity assuaged.
I had thought that both ends of the Screen printer cable would be 40 pin, 
That's why I had speculated on Model 3.
But I never spent $599 for one.
(instead, I struggled with interfacing a DTC-300 HyType 1 serial printer)

> I just cheked both the manual and looked at the E/I itself and the Line
> Printer Port is 34 pins and Centronics signals so no special cable there.
> I know that was the case on the Model 3 and Model 4.

Yes, the model 1, 3, and 4 parallel printer ports ("Line Printer Port") 
are essentially the same.  If you examine the circuitry in the interfaces, 
you might not think that they are "similar" :-)    They all use the 
#26-1401 printer cable (34 pin IDC card-edge to 36 pin "blue ribbon")

My homemade 34 pin to 50 pin cables for 8" drives (crimp with a couple of 
wires moved) is functionally similar to D-Bit's FDADAP, but electrically 
dissimilar, in that I don't implement TG43, when used in a read-only 
situation.   If that were to have been available at the time, it would 
have saved me a lot of wasted time bread-boarding a totally unnecessary 

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