W77LE58_07 Datasheet, PDF (34/82 Pages) Winbond – 8-BIT MICROCONTROLLER

W77LE58/W77L058A
6.2 InstructionTiming
The instruction timing for the W77L058 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 W77L058 and the standard 8032. In the W77L058 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 W77L058
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 W77L058 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 W77L058, 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 W77L058, based on the number of machine
cycles, there are five different types, while in the standard 8032 there are only three. However, in the
W77L058 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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