INTEL 8080 Chip
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"M.Shima [21] was the 8080 project
manager under Faggin. My specification used all 256 operation codes,
and 12th from the bottom of my list was an obscure instruction (XTHL)
for exchanging the top of stack with the HL register pair. This
instruction required five memory cycles to execute, and would be used
to pass arguments to subroutines. I carefully explained each
instruction to Shima, whose patience was tested as I detailed the XTHL
operation. He drew a line under this instruction, and declared:
This is why the last 12 instructions were never implemented and why there was room in the instructions set for the 8085 microprocessor's added instructions [23]." Stanley Mazor "The History of the Microcomputer - Invention and Evolution" |
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| Intel 8080 Die - Courtesy of Stanley Mazor |
