<SOMEWHAT-OFF-TOPIC-REMINISCE>

>> The VT320 don't have graphics, but it has software dowloadable
>> character sets.  Now guess how it does graphics...

> Does *everyone* build these things???  Built one myself in college ;-)

This reminds me of something I did once.

I have a handful of TeleVideo terminals.  One of them - the 955 - has a
digital electronics board that's relatively easy to remove from the
rest of the terminal.

It has three EPROMS on it, and a 65SC802 CPU.  I pulled the ROMs and
dumped them.  It turned out that one of them held the bulk of the
terminal's code, one was for user-supplied terminal firmware (and
there's an escape sequence, documented in the manual, for calling said
user-supplied firmware - though no doco on the interface specs needed
to actually write said firmware), and the third was character bitmaps.

I meddled.  I replaced the character bitmaps to give the terminal an
8859-1 font rather than the not-quite-8859-1 font it had before, and
also clean up some aesthetic issues with characters I wasn't otherwise
messing with.  I also pored over the firmware enough to figure some of
the hardware interfaces out and built code for the user firmware
socket; I then had a video game that ran entirely in the terminal.  (It
wasn't a particularly interesting video game; it was a slight variant
of worm(6).  It was mainly proof-of-concept.  It drew razzing from a
friend about when I was going to have NetBSD/tvi955 working.)

The reason I mention it in this thread is that when I was experimenting
with the font ROM, one thing I did was to run wire jumpers from the
font ROM socket to a breadboard, where I put the old ROM and some
static RAM, with glue logic to select one or the other; I then also
added more glue logic and a serial line interface, so that by sending
characters down a serial line (not the one connected to the terminal) I
could write to the RAM.

This then gave me downloadable character bitmaps. :-)  (All the extra
wires and glue logic meant that I got some snow on the screen; it seems
the data didn't always get to the video circuitry in time.  Otherwise I
would have done it for the user-firmware ROM too - but while getting
bits wrong occasionally is acceptable for a font ROM, it would not be
very workable for a code ROM.)

</SOMEWHAT-OFF-TOPIC-REMINISCE>

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