The paper tape loader ROM will actually 'work', if your 12531 interface
board happens to power-up in receive mode.
Or if you run a small program to write a control word to the 12531 prior
to running the loader ROM code (without pressing PRESET) you could
put the board into receive mode and run the loader.
But 12531 boards are slow, and not the most reliable. They often drop
characters when jumpered for higher baud rates.
But small program can indeed be loaded this way, at least sometimes!
----- Original Message -----
From: "Jay West" <jwest at classiccmp.org>
To: "General Discussion: On-Topic and Off-Topic Posts"
<cctalk at classiccmp.org>
Sent: Monday, January 08, 2007 10:25 PM
Subject: Re: HP 21MX/F and OS choices (was Lookee what I just got!)
I found that serial booting the system to be the
easiest way to get
started. I don't recall which one but, one of the loader ROMS will work
with the "high speed serial" card and read data off a serial link.
I don't recall any loader rom working with a 12531 HS TERM board. I could
well be wrong though, it's been WAY too long since I had my head firmly in
HP-world. You CAN do it with a 264x (terminal) loader rom and a BACI
board - as Bob S. said. If there is a loader rom that happens to work with
the 12531 (ie, if the 12531 happens to have the same programmatic
interface as say... the paper tape board...) I'd like to know. I just
don't have time to go test it :)
There's no handshaking or error correction
but, with a short RS232 link,
passing data is not a problem. The ABS data format does provide checksum
error detection so data errors will be detected.
Careful there... checksum (mod256) does NOT catch transposition of
bytes/words, missing all zero words/bytes, extra all zero words/bytes, and
identical bits swapped between words/bytes. There is a length field
included in the ABS format so that will catch missing or extra nulls. But
it still won't catch the other errors.