PC8E interface to other tape readers?

Charles charlesmorris800 at centurytel.net
Tue Sep 29 10:44:27 CDT 2015

The 8/A's power supply, RL02's and RX01 is all working fine (knocking on 
wood)... so far, no return of the dreaded Power OK "flicker". Maybe it 
really is fixed this time.. Famous last words, I know!

Now I am pondering my PC8E (M840) reader/punch control board, and a Slo-Syn 
TRP125 reel-to-reel 1" 8-bit paper tape reader that's been sitting unused in 
my other rack, probably for at least ten years when I got it very cheap. I'm 
thinking of interfacing them since I don't have a PC04 and no pressing need 
(or money) for one. The TRP125 can do 125 characters per second, not as good 
as the 300 of the PC04 but still much faster than the ASR-33 if I feel like 
messing with paper tapes...

The drive just needs a pulse to move the tape. Data can be read/strobed into 
the PC8E register almost any time the tape is not actually moving. (A real 
PC04 has a stepper motor controlled by the PC8E, so one of those four step 
outputs will probably work as a move pulse). Doubt I'd ever need to back up 
the tape one character.
Timing will probably need to be adjusted for some pulse widths and the rep 
rate which is slower. (1 byte is 8 ms on this one but 3.33 ms on the PC04. 
The no-tape timeout of the PC8E is 10 ms).

One thing missing from the TRP125 is a tape-out indication and motor stop, 
though. The TRP125 reel drive motors keep spinning until the tension arms 
are manually raised to a detent position that actuates microswitches to turn 
the motors off. The ASR-33 stops automatically when the tape has run out, 
which would be useful. I suppose I could add a microswitch to sense the 
presence of tape, or perhaps an LED/photocell to read the sprocket holes and 
provide pulses as the PC04 does. Otherwise I'd have to "fake" the feed hole 
pulses and manually shut the reader off once the tape runs out.

I'd like to hear from anyone who's done something similar to interface a 
non-DEC tape reader.

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