[TUHS] flaky webster or sigma WQESD4 and RQD11 controllers on KA650???

John Holden johnh at psych.usyd.edu.au
Sat Dec 14 12:30:13 AEST 2002

Early ROM revisions on the Webster MSCP controllers were too slow for the
KA650 and would often loose interrupts (amoungst other things). Signals such
as NPR and BR grants were polled from a pseudo microcode loop which took too

The RS232 interface doesn't use standard receivers. Check for a 5 volt zener on
the input of an 74LS240 (from the 10 pin i/o connector) and add a schottky
in parallel (a 1N5818 would do) if one isn't there

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