CAT28C256
DATA Polling
Toggle Bit
DATA polling is provided to indicate the completion of
write cycle. Once a byte write or page write cycle is
initiated, attempting to read the last byte written will
output the complement of that data on I/O7 (I/O0–I/O6
are indeterminate) until the programming cycle is com-
plete. Upon completion of the self-timed write cycle, all
I/O’s will output true data during a read cycle.
InadditiontotheDATAPollingfeatureoftheCAT28C256,
the device offers an additional method for determining
the completion of a write cycle. While a write cycle is in
progress, reading data from the device will result in I/O6
togglingbetweenoneandzero. However, oncethewrite
is complete, I/O6 stops toggling and valid data can be
read from the device.
Figure 7. DATA Polling
ADDRESS
CE
WE
t
OEH
t
OES
t
OE
OE
t
WC
= X
I/O
D
= X
D
D
= X
OUT
7
IN
OUT
28C256 F10
Figure 8. Toggle Bit
WE
CE
OE
t
OEH
t
OES
t
OE
(1)
(1)
I/O
6
t
WC
28C256 F11
Note:
(1) Beginning and ending state of I/O is indeterminate.
6
Doc. No. 25020-0A 2/98
8
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