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Semiconductor Group
3-4
1998-04-01
CPU Timing
C500 Family
Figure 3-2
External Program Memory Fetches
3.2.2 Accessing External Data Memory
The port 2 drivers use the strong pullups during the entire time that they are emitting address bits
that are 1«s. This occurs when the MOVX @DPTR instruction is executed and when external
program fetches are executed. During this time the port 2 latch (the special function register) does
not have to contain 1«s, and the contents of the port 2 SFR are not modified. If the external memory
cycle is not immediately followed by another external memory cycle, the undisturbed contents of the
port 2 SFR will reappear in the next cycle.
and
show in detail the timings of the external data memory read and write cycles.
MCD02772
S1
P1 P2
P2
P1
S2
P2
P1
S3
P2
P1
S4
P2
P1
S5
P2
P1
S6
P2
P1
S1
P2
P1
S2
ALE
PSEN
P0
PCL
Out
PCL
PCL
P2
PCH Out
Data
Sampled
Sampled
Data
Sampled
Data
States
Out
Out
PCH Out
PCH Out