W925EP01 Datasheet, PDF (98/108 Pages) Winbond – 8-BIT CID MICROCONTROLLER

W925EP01/ W925EP01FG
Timing Waveforms, continued
Data Write Cycle
CLK
PSEN
WR
D7-D0
A16-A0
Last Cycle
of Previous
Instruction
First
Machine cycle
Second
Machine cycle
MOVX instruction cycle
Next Instruction
Machine Cycle
C1 C2 C3 C4 C1 C2 C3 C4 C1 C2 C3 C4 C1 C2 C3 C4
D7-D0
D7-D0
D7-D0
MOVX Inst.
Address
Next Inst.
Address
MOVX Data
Address
MOVX Inst.
Next Inst. Read ^{MOVX Data out}
A16-A0
A16-A0
A16-A0
D7-D0
A16-A0
7.1 Instruction Timing
The instruction timing for the W925EP01 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 W925EP01 and the standard 8032. In the W925EP01 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
W925EP01 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 W925EP01 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 instruction, 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 W925EP01, 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.
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