From f16df5983c908fc1f9a6136fff0859e342e9af56 Mon Sep 17 00:00:00 2001 From: Ben Harris Date: Wed, 11 Dec 2024 22:34:53 +0000 Subject: [PATCH] Some notes on TIFAX --- NOTES | 33 +++++++++++++++++++++++++++++++++ 1 file changed, 33 insertions(+) diff --git a/NOTES b/NOTES index 78fdb3e..f573325 100644 --- a/NOTES +++ b/NOTES @@ -257,3 +257,36 @@ P 𜹇 Q 𜹈 R 𜹉 S 𜹊 T 𜹋 U 𜹌 V 𜹍 W 𜹎 X 𜹏 Y 𜹐 Z ▘ [ ▝ \ ▖ ] ▗ ^ ▀ _ ▌ Looks like Unicode has somehow missed out one of them. + +TIFAX +===== + +The TIFAX XM11 was a 1975 Teletext decoder board made by Texas +Instruments Ltd. It used a 5 × 9 character matrix with rounding like +an SAA5050, but implemented over rather more chips. Unlike the +SAA5050, the XM11 had two black pixels horizontally between +characters, so the total character size was 7 × 10. + +https://www.blunham.com/Radar/Teletext/PDFs/XM11-B183.pdf + +The character ROM is an SN74S262, and the character shapes mostly +match the SAA5050, so treating it as a variant might not be +unreasonable. There is some uncertainty over some characters as +explained by Neil Williamson: https://p298.net/devnotes/ + +The different character pitch could mostly be accomodated by having +the application add extra spacing between characters, but what about +mosaic graphics? The XM11 generated those in a separate chip (the +X908), and they were the full 7 pixels wide, four in the left column +and three in the right. Would we want an entire extra set? At least +the XM11 didn't support separated graphics (added in the 1976 spec). +And what about box-drawing? + +The XM11 has a dot clock the same as the Teletext bit clock: 6.9735 MHz. +Hence a nominal XPIX of 105.8. + +There was also a Swedish ROM, SN74S263, which was used in the ABC80, a +Swedish Z80-based computer, so there is a purported ROM of it +available for emulators. + +Also some real screenshots; e.g. https://www.youtube.com/watch?v=Jy6tQsyd4ho -- 2.30.2