80C186EA/80C188EA, 80L186EA/80L188EA
80C186EA/80C188EA EXECUTIONTIMINGSA determination of program exeuction timing must
consider the bus cycles necessary to prefetch in-
structions as well as the number of execution unit
cycles necessary to execute instructions. The fol-
lowing instruction timings represent the minimum
execution time in clock cycle for each instruction.
The timings given are based on the following as-
sumptions:
#The opcode, along with any data or displacement
required for execution of a particular instruction,
has been prefetched and resides in the queue at
the time it is needed.
#No wait states or bus HOLDs occur.
#All word-data is located on even-address bound-
aries. (80C186EA only)
All jumps and calls include the time required to fetch
the opcode of the next instruction at the destination
address.
All instructions which involve memory accesses can
require one or two additional clocks above the mini-
mum timings shown due to the asynchronous hand-
shake between the bus interface unit (BIU) and exe-
cution unit.
With a 16-bit BIU, the 80C186EA has sufficient bus
performance to endure that an adequate number of
prefetched bytes will reside in the queue (6 bytes)
most of the time. Therefore, actual program exeuc-
tion time will not be substanially greater than that
derived from adding the instruction timings shown.
The 80C188EA 8-bit BIU is limited in its performance
relative to the execution unit. A sufficient number of
prefetched bytes may not reside in the prefetch
queue (4 bytes) much of the time. Therefore, actual
program execution time will be substantially greater
than that derived from adding the instruction timings
shown.
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