[GreenKeys] Simulating M33/35 teletypes hooked to computers like in the 70s

[John Nagle]

On 8/30/2012 9:03 AM, greenkeys-request at mailman.qth.net wrote:
> From: Keelan Lightfoot <keelan at grenander.com> Subject: Re:
> [GreenKeys] Feeding ITTY to the teletype;	simulating M33/35 teletypes
> hooked to computers like in the 70s To: <gil at baudot.net>
> <gil at baudot.net> Cc: aaa-greenkeys <greenkeys at mailman.qth.net>,
> William Bytheway <k7tty at q.com> Message-ID:
> <805C7147-56C8-411A-BD50-D5E15700B09C at grenander.com> Content-Type:
> text/plain; charset=us-ascii
> 
> Gil,
> 
> The serial drivers for the UART on the X-Port support 5 to 8 bit
> codes, but the driver (and the Linux serial subsystem) doesn't
> support 45.45 baud. Fortunately, the UART in the X-Port is quite
> flexible, and it can be configured to talk at 45.45 baud with very
> little work.

    Model 33 and 35 machines talk ASCII, of course, usually at 110
baud.  Those can be plugged directly into serial ports on most
computers.  Wost case, you need a 20mA current loop converter.
If you're running Linux, you can configure them as a console and
log in.

    I have Python code for running Baudot machines.  See

	http://www.aetherltd.com/communicating.html
	http://sourceforge.net/projects/baudotrss/

For an 60mA electrical connection I use

	http://www.aetherltd.com/connecting.html
	http://www.aetherltd.com/connectingusb.html

and an off the shelf solution is

	http://www.telebyteusa.com/catalog/products/65a.htm

One problem with USB to serial converters is that they tend to
have too much output side buffering for slow lines, often
hundreds of bytes.  Ethernet to serial converters may have
megabytes of buffering.  If you try to interrupt output,
you may have to wait for the buffer to flush.  Baudotrss
handles this; on receiving a BREAK, the UART is flushed.
Also, for motor power control, you have to calculate how
much data is still in the buffer and allow extra time for
printing to finish before cutting motor power.

Decoding FSK in software has been done many times.  There are
packages around for that, some of which are open source.

			John Nagle