DATA Polling and Toggle Bit for End of Write Detection

DATA POLLING: The AT28C64B features DATA Polling
to indicate the end of a write cycle. During a byte or page
write cycle an attempted read of the last byte written will
result in the complement of the written data to be presented
on I/O7. Once the write cycle has been completed,
true data is valid on all outputs, and the next write cycle
may begin. DATA Polling may begin at any time during the
write cycle.

TOGGLE BIT: In addition to DATA Polling, the AT28C64B
provides another method for determining the end of a write
cycle. During the write operation, successive attempts to
read data from the device will result in I/O6 toggling between
one and zero. Once the write has completed, I/O6
will stop toggling, and valid data will be read. Toggle bit
reading may begin at any time during the write cycle.