W77LE532_07 Datasheet, PDF (33/88 Pages) Winbond – 8-BIT MICROCONTROLLER

W77LE532/W77L532A
8. INSTRUCTION TIMING
The instruction timing for the W77L532 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 W77L532 and the standard 8032. In the W77L532 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
W77L532 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 W77L532 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 W77L532, 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 W77L532, based on the
number of machine cycles, there are five different types, while in the standard 8032 there are only
three. However, in the W77L532 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: February 1, 2007
Revision A7