Workings of a TTY

From: Tony Duell <ard_at_odin.phy.bris.ac.uk>
Date: Mon Dec 1 11:39:53 1997

On Sun, 30 Nov 1997, Hans B Pufal wrote:

> I have a query about the operation of a KSR 33 TTY when reading paper
> tape : does the TTY blindly send the characters read from the tape at 10
> cps or is the tape advance and read triggered by a signal from whatever
> th TTY is connected to.

I'll guess you mean an ASR33 - the KSR is the keyboard send/recieve and
doesn't have the punch or reader.

The basic ASR simply sends the tape at 10cps under the control of the
manual switch on the reader. Turning this switch on energises a solenoid
at the back which releases the transmit clutch. This serialises the bits
from the reader, and once every revolution it closes a pair of contacts
that trigger a solenoid in the reader to step the tape on by one character

According to the Model33 partsbook there's an option that adds a couple of
rails in the function box ('stunt box'for people brought up on Creeds
:-)) These respond to XON and XOFF and close/open a pair of contacts that
are wired into the reader run circuit (you'd need a diagram to see how,
since you get auto and manual control IIRC). That gives you a remote
reader control in the obvious way.

A number of computer manufacturers - I have notes from DEC and Intel -
modified ASR33's for their computers. This mod generally consisted of
fitting a reed relay in series with the reader trip solenoid and
controlling it from the computer's serial I/O interface circuit in some
way. Most of these mods were very similar, and were used to single-step
the reader when loading a tape.

I've also got a Data Dynamics tty which is an ASR33's mechanics in a new
case with a Data Dynamics electronic module. This gives RS232 and current
loop serial interfaces _and_ single-stepping of the reader both from a
button on the panel and remotely.

Hope that helps. I can probably find diagrams of the above if you need
them.


> Hans B. Pufal : <mailto:hansp_at_digiweb.com>

-tony
Received on Mon Dec 01 1997 - 11:39:53 GMT

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