AM28F020 Advanced Micro Devices, AM28F020 Datasheet - Page 20

• Manufacturer Part Number: AM28F020
• Description: 2 Megabit (256 K x 8-Bit) CMOS 12.0 Volt/ Bulk Erase Flash Memory
• Manufacturer: Advanced Micro Devices

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
Am28F020
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.