13 Jul
2005
13 Jul
'05
7:41 p.m.
>>>> "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.
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