W77L532A Datasheet, PDF (38/88 Pages) List of Unclassifed Manufacturers – 8-BIT MICROCONTROLLER

W77L532A
External Data Memory Access Timing:
The timing for the MOVX instruction is another feature of the W77L532. In the standard 8032, the
MOVX instruction has a fixed execution time of 2 machine cycles. However in the W77L532, 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
W77L532 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.
Table 4. Data Memory Cycle Stretch Values
M2
M1
M0
MACHINE
CYCLES
0
0
0
2
0
0
1
3 (default)
0
1
0
4
0
1
1
5
1
0
0
6
1
0
1
7
1
1
0
8
1
1
1
9
RD OR WR
STROBE WIDTH IN
CLOCKS
2
4
8
12
16
20
24
28
RD OR WR STROBE
WIDTH @ 25 MHZ
80 nS
160 nS
320 nS
480 nS
640 nS
800 nS
960 nS
1120 nS
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