W79E217A Datasheet, PDF (83/207 Pages) Winbond – 8-bit Microcontroller

Preliminary W79E217A Data Sheet
nine machine cycles. The default value is one, resulting in a MOVX instruction of three machine
cycles.
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
3 (default)
4
5
6
7
8
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
RD _OR WR
STROBE WIDTH
@ 33 MHZ
60.6 nS
121.2 nS
242.2 nS
363.6 nS
484.8 nS
606.1 nS
727.3 nS
848.5 nS
Table 8-2: Data Memory Cycle Stretch Values
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: December 14, 2007
Revision A3.0