Rainbow Electronics AT25F1024 - Manual (Page 9)

9
AT25F512/1024
1440P–SEEPR–6/04
The WRSR instruction also allows the user to enable or disable the Write Protect (WP)
pin through the use of the Write Protect Enable (WPEN) bit. Hardware write protection is
enabled when the WP pin is low and the WPEN bit is “1”. Hardware write protection is
disabled when either the WP pin is high or the WPEN bit is “0.” When the device is hard-
ware write protected, writes to the Status Register, including the Block Protect bits and
the WPEN bit, and the locked-out sectors in the memory array are disabled. Write is
only allowed to sectors of the memory which are not locked out. The WRSR instruction
is self-timed to automatically erase and program BP0, BP1, and WPEN bits. In order to
write the status register, the device must first be write enabled via the WREN instruction.
Then, the instruction and data for the three bits are entered. During the internal write
cycle, all instructions will be ignored except RDSR instructions. The AT25F512/1024 will
automatically return to write disable state at the completion of the WRSR cycle.
Note: When the WPEN bit is hardware write protected, it cannot be changed back to “0”, as
long as the WP pin is held low.
READ* (READ): Reading the AT25F512/1024 via the SO (Serial Output) pin requires
the following sequence. After the CS line is pulled low to select a device, the READ
instruction is transmitted via the SI line followed by the byte address to be read (Refer to
Table 6). Upon completion, any data on the SI line will be ignored. The data (D7-D0) at
the specified address is then shifted out onto the SO line. If only one byte is to be read,
the CS line should be driven high after the data comes out. The READ instruction can
be continued since the byte address is automatically incremented and data will continue
to be shifted out. For the AT25F1024, when the highest address is reached, the address
counter will roll over to the lowest address allowing the entire memory to be read in one
continuous READ instruction. For the AT25F512, the read command must be termi-
nated when the highest address (00FFFF) is reached.
PROGRAM (PROGRAM): In order to program the AT25F512/1024, two separate
instructions must be executed. First, the device must be write enabled via the WREN
instruction. Then the PROGRAM instruction can be executed. Also, the address of the
memory location(s) to be programmed must be outside the protected address field loca-
tion selected by the Block Write Protection Level. During an internal self-timed
programming cycle, all commands will be ignored except the RDSR instruction.
The PROGRAM instruction requires the following sequence. After the CS line is pulled
low to select the device, the PROGRAM instruction is transmitted via the SI line followed
by the byte address and the data (D7-D0) to be programmed (Refer to Table 6). Pro-
gramming will start after the CS pin is brought high. The low-to-high transition of the CS
pin must occur during the SCK low time immediately after clocking in the D0 (LSB) data
bit.
Table 5. WPEN Operation
WPEN WP WEN ProtectedBlocks UnprotectedBlocks Status Register
0 X 0 Protected Protected Protected
0 X 1 Protected Writable Writable
1 Low 0 Protected Protected Protected
1 Low 1 Protected Writable Protected
X High 0 Protected Protected Protected
X High 1 Protected Writable Writable