X5648 Datasheet, PDF (7/18 Pages) Intersil Corporation – CPU Supervisor with 64Kbit SPI EEPROM

Figure 5. Read EEPROM Array Sequence
CS
X5648, X5649
SCK
0 1 2 3 4 5 6 7 8 9 10
20 21 22 23 24 25 26 27 28 29 30
Instruction
SI
16 Bit Address
15 14 13
3210
High Impedance
SO
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 opera-
tion. 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 regis-
ter or EEPROM sequence, the status register may be
read to check the WIP bit. During this time the WIP bit
will be high.
Data Out
7 654321 0
MSB
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.
7
FN8136.0
March 17, 2005