New Xmodem Device Handlers for OS/8

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Martin Eberhard

Sep 5, 2020, 4:22:17 PM9/5/20
I've written and tested a set of OS/8 device handlers that send and receive data via a KL8-E-type serial port, using the Xmodem protocol. These make it really easy to upload and download any type of OS/8 file.

Xmodem is handy for this because it provides reliable in-band handshaking that will work with pretty much any system. Additionally, there are plenty of Xmodem programs for all common operating systems, including Windows, MacOS, and Linux, so no custom program is required on the other end. (I use TeraTerm, which works great.)

Use these handlers with for example PIP (always with the /I option, regardless of file type):

*XMTA:<MYFILE.LS/I {for an ASCII file}

XMR will receive a file (of any type), behaving pretty much like a PTR device handler.
XMT0 will transmit a file (of any type), pretty much like a PTP device handler.
XMTA is like XMT0, except that it strips the parity bit, handy for ASCII files.

I've also written an extensive manual for these handlers.

You can find the handlers and documentation here:

Testing was done on a real PDP-8/e, with DECtape as the system device, and transferring data via a modified M8650, at 38400 baud. Nice and fast (at least until the tape needs to spool halfway across its length!) , and the flow control works perfectly, of course.

Comments are most welcome!


Thomas Moss

Sep 6, 2020, 8:49:59 PM9/6/20
to Martin Eberhard

Very nice! Just as I was thinking about doing something similar myself
too, heh. (although as a standalone program rather than a handler)

I'll be sure to give it a try soon.

SDF Public Access UNIX System -
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