The device contains an Auto Select operation to sup-
plement traditional PROM programming methodology.
The operation is initiated by writing 80h or 90h into the
command register. Following this command, a read
cycle address 0000h retrieves the manufacturer code
of 01h. A read cycle from address 0001h returns the
device code. To terminate the operation, it is necessary
to write another valid command, such as Reset (FFh),
into the register.
Auto Select Command
AMD’s Flash memories are designed for use in applica-
tions where the local CPU alters memory contents. Ac-
cordingly, manufacturer and device codes must be
accessible while the device resides in the target sys-
tem. PROM programmers typically access the signa-
ture codes by raising A9 to a high voltage. However,
multiplexing high voltage onto address lines is not a
generally desired system design practice.
20
Am28F256
AMD [ AMD ]
