9
FN8130.2
June 15, 2006
Read Sequence
When reading from the EEPROM memory array, CS is first
pulled low to select the device. The 8-bit READ instruction is
transmitted to the device, followed by the 16-bit address.
After the READ opcode and address are sent, the data
stored in the memory at the selected address is shifted out
on the SO line. The data stored in memory at the next
address can be read sequentially by continuing to provide
clock pulses. The address is automatically incremented to
the next higher address after each byte of data is shifted out.
When the highest address is reached, the address counter
rolls over to address $0000 allowing the read cycle to be
continued indefinitely. The read operation is terminated by
taking CS
high. Refer to the read EEPROM array sequence
(Figure 1).
To read the status register, the CS
line is first pulled low to
select the device followed by the 8-bit RDSR instruction.
After the RDSR opcode is sent, the contents of the status
register are shifted out on the SO line. Refer to the read status
register sequence (Figure 2).
Write Sequence
Prior to any attempt to write data into the device, the “Write
Enable” Latch (WEL) must first be set by issuing the WREN
instruction (Figure 3). CS
is first taken LOW, then the WREN
instruction is clocked into the device. After all eight bits of the
instruction are transmitted, CS
must then be taken HIGH. If
the user continues the write operation without taking CS
HIGH after issuing the WREN instruction, the write operation
will be ignored.
To write data to the EEPROM memory array, the user then
issues the WRITE instruction followed by the 16 bit address
and then the data to be written. Any unused address bits are
specified to be “0’s”. The WRITE operation minimally takes
32 clocks. CS
must go low and remain low for the duration of
the operation. If the address counter reaches the end of a
page and the clock continues, the counter will roll back to the
first address of the page and overwrite any data that may
have been previously written.
For the page write operation (byte or page write) to be
completed, CS
can only be brought HIGH after bit 0 of the
last data byte to be written is clocked in. If it is brought HIGH
at any other time, the write operation will not be completed
(Figure 4).
To write to the status register, the WRSR instruction is
followed by the data to be written (Figure 5). Data bits 0 and
1 must be “0”.
While the write is in progress following a status register or
EEPROM sequence, the status register may be read to
check the WIP bit. During this time the WIP bit will be high.
Operational Notes
The device powers-up in the following state:
• The device is in the low power standby state.
• A HIGH to LOW transition on CS
is required to enter an
active state and receive an instruction.
• SO pin is high impedance.
• The write enable latch is reset.
• The flag bit is reset.
• Reset signal is active for t
PURST
.
Data Protection
The following circuitry has been included to prevent
inadvertent writes:
• A WREN instruction must be issued to set the write enable
latch.
•CS
must come HIGH at the proper clock count in order to
start a nonvolatile write cycle.
X5168, X5169
