W79E632A Datasheet, PDF (29/79 Pages) Winbond – 8-BIT MICROCONTROLLER

W79E632A/W79L632A
Instruction Fetch Operand Fetch
Operand Fetch
Operand Fetch
Operand Fetch
C1 C2 C3 C4 C1 C2 C3 C4 C1 C2 C3 C4 C1 C2 C3 C4 C1 C2 C3 C4
CLK
ALE
PSEN
AD7-0
A7-0 OP-CODE
A7-0 ^OPERAND
A7-0 OPERAND
A7-0 OPERAND
A7-0 OPERAND
PORT 2
Address A15-8
Address A15-8
Address A15-8
Address A15-8
Address A15-8
Figure 7. Five Cycle Instruction Timing
7.1.1 External Data Memory Access Timing
The timing for the MOVX instruction is another feature of the W79E(L)632. In the standard 8032, the
MOVX instruction has a fixed execution time of 2 machine cycles. However in the W79E(L)632, the
duration of the access can be varied by the user.
The instruction starts off as a normal op-code fetch of 4 clocks. In the next machine cycle, the
W79E(L)632 puts out the address of the external Data Memory and the actual access occurs here. The
user can change the duration of this access time by setting the STRETCH value. The Clock Control SFR
(CKCON) has three bits that control the stretch value. These three bits are M2-0 (bits 2-0 of CKCON).
These three bits give the user 8 different access time options. The stretch can be varied from 0 to 7,
resulting in MOVX instructions that last from 2 to 9 machine cycles in length. Note that the stretching of
the instruction only results in the elongation of the MOVX instruction, as if the state of the CPU was held
for the desired period. There is no effect on any other instruction or its timing. By default, the Stretch
value is set at 1, giving a MOVX instruction of 3 machine cycles. If desired by the user the stretch value
can be set to 0 to give the fastest MOVX instruction of only 2 machine cycles.
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Publication Release Date: Nov. 11, 2009
Revision A10