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80C186EC 188EC 80L186EC 188EC
80C186EC 80C188EC EXECUTION
TIMINGS
A determination of program execution 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 cycles 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 (80C186EC only)
All jumps and calls include the time required to fetch
the opcode of the next instruction at the destination
address
50
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 80C186EC has sufficient bus
performance to ensure that an adequate number of
prefetched bytes will reside in the queue (6 bytes)
most of the time Therefore actual program execu-
tion time will not be substantially greater than that
derived from adding the instruction timings shown
The 80C188EC 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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