W77IE58 Datasheet, PDF (41/90 Pages) Winbond – 8-BIT MICROCONTROLLER

Preliminary W77IE58
Instructiion Timing
The instruction timing for the W77IE58 is an important aspect, especially for those users who wish to
use software instructions to generate timing delays. Also, it provides the user with an insight into the
timing differences between the W77IE58 and the standard 8032. In the W77IE58 each machine cycle is
four clock periods long. Each clock period is designated a state. Thus each machine cycle is made up
of four states, C1, C2 C3 and C4, in that order. Due to the reduced time for each instruction execution,
both the clock edges are used for internal timing. Hence it is important that the duty cycle of the clock
be as close to 50% as possible to avoid timing conflicts. As mentioned earlier, the W77IE58 does one
op-code fetch per machine cycle. Therefore, in most of the instructions, the number of machine cycles
needed to execute the instruction is equal to the number of bytes in the instruction. Of the 256 available
op-codes, 128 of them are single cycle instructions. Thus more than half of all op-codes in the W77IE58
are executed in just four clock periods. Most of the two-cycle instructions are those that have two byte
instruction codes. However there are some instructions that have only one byte instructions, yet they are
two cycle instructions. One instruction which is of importance is the MOVX instruction. In the standard
8032, the MOVX instruction is always two machine cycles long. However in the W77IE58, the user has a
facility to stretch the duration of this instruction from 2 machine cycles to 9 machine cycles. The RD
and WR strobe lines are also proportionately elongated. This gives the user flexibility in accessing both
fast and slow peripherals without the use of external circuitry and with minimum software overhead. The
rest of the instructions are either three, four or five machine cycle instructions. Note that in the W77IE58,
based on the number of machine cycles, there are five different types, while in the standard 8032 there
are only three. However, in the W77IE58 each machine cycle is made of only 4 clock periods compared
to the 12 clock periods for the standard 8032. Therefore, even though the number of categories has
increased, each instruction is at least 1.5 to 3 times faster than the standard 8032 in terms of clock
periods.
CLK
ALE
PSEN
AD7-0
PORT 2
Single Cycle
C1
C2
C3
C4
A7-0
Data_ in D7-0
Address A15-8
Figure 3. Single Cycle Instruction Timing
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Publication Release Date: July 2000
Revision A1