An interesting use of the 4004 instructions
dkelvey at hotmail.com
Thu Dec 15 13:52:49 CST 2016
I was looking at some disassembled 4004 code when I came across
a SKIP operation.
It isn't normally an instruction but If you do a JCN with all the CCCC = 0,
it will do a NEVER jump.
This is the equivalent of a SKIP instruction.
I would suppose a JCN with CCCC = $8000 would be an always jump,
on page ( not real useful as JUN takes the same cycles and space ).
I thought at first there was some errors in the code because there
were JMS to the middle of JCN instruction but then I noticed that there
were no conditions specified for the JCN. A little thought and I realized
it was a way to skip over a single byte instruction.
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