[pdp7-unix] Running cas

Lars Brinkhoff lars at nocrew.org
Mon Oct 21 17:37:14 AEST 2019


Another interesting piece of information from cas.

The last line in the output for each character looks like label=x-b+number.
Number is an 18-bit value where the top two bits are always "01", then
six bits for the number of 6-bit bytes, and finally 10 zero bits.  The
last bits are presumably an offset which comes from x-b.

My guess would be that the WCGA instruction passes an address to the
character generator.  At this address is a table of words formatted
according to the previous paragraph.  And somewhere near this is the
actual character shape words.

I have noted that the WCGA address is octal 6000, and the kernel ends
right below this.  I haven't seen anything that fits the description of
the character generator table.  E.g. searching for "amper" doesn't turn
up anything useful.


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