Registers A1 and B6
Fetch leaves CDC machine addresses in registers so that they need not be
recomputed from a PDP-8 format address in a subsequent store. For example,
the ISZ (increment and skip if zero) instruction handler computes the physical
address parameters from X3 only once.
Between these to macro expansions A1 contains the address of a word
block and B6 contains the shift count required to isolate the desired word
within the block. See other register assignments.
© 1975, 1998, Ward Cunningham
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