X28C256
DATA
POLLING I/O
7
Figure 2.
DATA
Polling Bus Sequence
LAST
WRITE
WE
CE
OE
VIH
I/O7
HIGH Z
VOL
An
An
An
An
An
An
An
3855 FHD F12
VOH
X28C256
READY
A0–A14
Figure 3.
DATA
Polling Software Flow
DATA
Polling can effectively halve the time for writing to
the X28C256. 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.
WRITE DATA
WRITES
COMPLETE?
YES
SAVE LAST DATA
AND ADDRESS
NO
READ LAST
ADDRESS
IO7
COMPARE?
YES
X28C256
READY
NO
3855 FHD F13
4