W79E225A_08 Datasheet, PDF (87/203 Pages) Winbond – 8-bit Microcontroller

Preliminary W79E225A/226A/227A Data Sheet
Stretching only affects the MOVX instruction. There is no effect on any other instruction or its timing; it
is as if the state of the CPU is held for the desired period. The timing waveforms when the stretch
value is zero, one, and two are shown below.
M2
0
0
0
0
1
1
1
1
M1
0
0
1
1
0
0
1
1
M0
0
1
0
1
0
1
0
1
MACHINE
CYCLES
2
RD OR WR
STROBE WIDTH
IN CLOCKS
2
RD OR WR
STROBE WIDTH
@ 25 MHZ
80 nS
3 (default)
4
160 nS
4
8
320 nS
5
12
480 nS
6
16
640 nS
7
20
800 nS
8
24
960 nS
9
28
1120 nS
Table 8-2: Data Memory Cycle Stretch Values
RD OR WR
STROBE WIDTH
@ 40 MHZ
50 nS
100 nS
200 nS
300 nS
400 nS
500 nS
600 nS
700 nS
CLK
ALE
PSEN
WR
PORT 0
PORT 2
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
A0-A7
D0-D7
A0-A7
D0-D7
A0-A7
D0-D7
A0-A7
D0-D7
MOVX Inst.
Address
Next Inst.
Address
MOVX Data
Address
MOVX Inst.
Next Inst. Read MOVX Data out
A15-A8
A15-A8
A15-A8
A15-A8
Figure 8-6: Data Memory Write with Stretch Value = 0
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Publication Release Date: April 15, 2008
Revision A4.0