W77C32_07 Datasheet, PDF (36/78 Pages) Winbond – 8-BIT MICROCONTROLLER

W77C32/W77C032A
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
8.2 MOVX Instruction
The W77C032, like the standard 8032, uses the MOVX instruction to access external Data Memory.
This Data Memory includes both off-chip memory as well as memory mapped peripherals. While the
results of the MOVX instruction are the same as in the standard 8032, the operation and the timing of
the strobe signals have been modified in order to give the user much greater flexibility.
The MOVX instruction is of two types, the MOVX @Ri and MOVX @DPTR. In the MOVX @Ri, the
address of the external data comes from two sources. The lower 8-bits of the address are stored in
the Ri register of the selected working register bank. The upper 8-bits of the address come from the
port 2 SFR. In the MOVX @DPTR type, the full 16-bit address is supplied by the Data Pointer.
Since the W77C032 has two Data Pointers, DPTR and DPTR1, the user has to select between the
two by setting or clearing the DPS bit. The Data Pointer Select bit (DPS) is the LSB of the DPS SFR,
which exists at location 86h. No other bits in this SFR have any effect, and they are set to 0. When
DPS is 0, then DPTR is selected, and when set to 1, DPTR1 is selected. The user can switch between
DPTR and DPTR1 by toggling the DPS bit. The quickest way to do this is by the INC instruction. The
advantage of having two Data Pointers is most obvious while performing block move operations. The
accompanying code shows how the use of two separate Data Pointers speeds up the execution time
for code performing the same task.
Block Move with single Data Pointer:
; SH and SL are the high and low bytes of Source Address
; DH and DL are the high and low bytes of Destination Address
; CNT is the number of bytes to be moved
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