Help needed: AS33 understanding Reader Run Control

From: Gerold Pauler <>
Date: Wed Feb 4 06:58:44 2004

it must have been far too late this morning.
After a little sleep,
I found out what went wrong.

Both sides HP in the Reader Run Control an I in the
RSR232 -> 20 mA converter made assumptions on how
the other end handles the signals.

HP thinks TX+ (positiv wire of transmit) is permanently
tied to Vcc and TX- is floating (on signal).
And RX- (negativ wire of receive) is permanently tied to
GND with TX+ floating.

I did it the other way - tying TX- to GND and RX+ to Vcc.

So the reader run control could not work.

I now will rework my converter box and show the result
(if wanted).

Thanks to all who answered

Gerold Pauler schrieb:
> Hi,
> in the process of restoring one of my teletypes I decided
> to connect it to a PC. Send and receive work fine, but the
> tape reader does NOT work in line mode (local is no problem).
> It is an ASR33 relabeled by HP and has a HP Reader Run Control Card.
> I have put a schematic of this card online
> (Couldn't figure out the types of T1 and D1 - so these can be a pnp or
> a zener diode also. Polarities of reader run signals (RDR+/RDR-) can
> also be wrong.)
> But I am too dump to understand how to connect the reader run signals.
> I'm not even sure what levels they should have.
> I just thought that a circuit identical to TX (on PC side aka RX on
> teletype) should do.
> If you need additional infos to help please let me know.
> Gerold (
Received on Wed Feb 04 2004 - 06:58:44 GMT

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