X28C64
DATA
Polling I/O
7
Figure 2.
DATA
Polling Bus Sequence
WE
LAST
WRITE
CE
OE
VIH
I/O7
HIGH Z
VOL
An
An
An
An
An
An
An
3853 FHD F12
VOH
X28C64
READY
A0–A12
Figure 3.
DATA
Polling Software Flow
DATA
Polling can effectively halve the time for writing to
the X28C64. The timing diagram in Figure 2 illustrates
the sequence of events on the bus. The software flow
diagram in Figure 3 illustrates one method of implement-
ing the routine.
NO
WRITE DATA
WRITES
COMPLETE?
YES
SAVE LAST DATA
AND ADDRESS
READ LAST
ADDRESS
IO7
COMPARE?
YES
X28C64
READY
NO
3853 FHD F13
4