Teleprint 390

[Tony Duell]

> 
> >>>>> "Jim" == Jim Beacon <jim at g1jbg.co.uk> writes:
> 
>  Jim> My 11/45 has a seperate "Paper Tape Advance" output on the
>  Jim> console serial interface, whic is set by writing to a register -
>  Jim> I assume that the Teleprint 390 / ASR33 has either a solenoid
>  Jim> drive or a clutch that allows the tape to advance one character
>  Jim> at a time, under processor control.
> 
> Bit 0 in the receive control register, right?  That's supposed to be
> the papertape reader "reader run" signal.  It isn't used as a one
> character at a time thing; it is read/write and if set remains set
> until explicitly cleared.

Are you sure? I was under the impression that setting that bit 
(conventionally done by INCing the appropriate location in the I/O page) 
would turn on the reader run relay, which would then be turned off when 
the card detected the start bit of the character. In other words it _is_ 
a character-at-a-time.


> 
> The idea is that the system would accept interactive input by leaving
> this bit clear, but then when you told it to read a papertape it would
> set the bit.  That starts the tape.  The program would then see
> characters streaming in.  At some point (perhaps when it sees a string
> of nulls, or when it knows the tape is finished by some internal
> coding) it would clear reader run again.
> 
> I don't know if this actually was used much.  The ASR33s I remember
> rarely if ever had this hooked up; the reader run control was done by
> flipping the papertape reader switch on the machine.

The reader run relay is not a standard Teletype fitment. It was a DEC 
modification, Intel and others had similar modifications too (and 
amazingly they werre all much the same). I believe, though, the Data 
Dynamics 390 has a reader control relay as part of the call control unit 
(which as I said is very different from the Teletype one). 

-tony