X25320
Write-Protect Enable
The Write-Protect-Enable (WPEN) is available for the
X25320 as a nonvolatile enable bit for the
WP
pin.
WPEN
WP
0
0
1
1
X
X
X
X
LOW
LOW
HIGH
HIGH
WEL
0
1
0
1
0
1
Blocks
Blocks
Register
Protected
Writable
Protected
Protected
Protected
Writable
3063 PGM T05.1
To read the status register the
CS
line is first pulled LOW
to select the device followed by the 8-bit RDSR instruc-
tion. After the RDSR opcode is sent, the contents of the
status register are shifted out on the SO line. The read
status register sequence is illustrated in Figure 2.
Write Sequence
Prior to any attempt to write data into the X25320, the
“write enable” latch must first be set by issuing the
WREN instruction (See Figure 3).
CS
is first taken LOW,
then the WREN instruction is clocked into the X25320.
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 E
2
PROM memory array, the user
issues the WRITE instruction, followed by the address
and then the data to be written. This is minimally a
thirty-two clock operation.
CS
must go LOW and remain
LOW for the duration of the operation. The host may
continue to write up to 32 bytes of data to the X25320.
The only restriction is the 32 bytes must reside on the
same page. If the address counter reaches the end of
the page and the clock continues, the counter will “roll
over” to the first address of the page and overwrite any
data that may have been written.
For the write operation (byte or page write) to be
completed,
CS
can only be brought HIGH after bit 0 of data
byte N is clocked in. If it is brought HIGH at any other time the
write operation will not be completed. Refer to Figures 4 and
5 below for a detailed illustration of the write sequences and
time frames in which
CS
going HIGH are valid.
To write to the status register, the WRSR instruction is
followed by the data to be written. Data bits 0, 1, 4, 5 and
6 must be “0”. This sequence is shown in Figure 6.
While the write is in progress following a status register
or E
2
PROM write sequence, the status register may be
read to check the WIP bit. During this time the WIP bit will
be HIGH.
Hold Operation
The
HOLD
input should be HIGH (at V
IH
) under normal
operation. If a data transfer is to be interrupted
HOLD
can be pulled LOW to suspend the transfer until it can be
resumed. The only restriction is the SCK input must be
LOW when
HOLD
is first pulled LOW and SCK must also
be LOW when
HOLD
is released.
The
HOLD
input may be tied HIGH either directly to V
CC
or tied to V
CC
through a resistor.
4
Protected Protected
Protected Writable
Protected Protected
Protected Writable
Protected Protected
Protected Writable
The Write Protect (WP) pin and the nonvolatile Write
Protect Enable (WPEN) bit in the Status Register control
the programmable hardware write protect feature. Hard-
ware write protection is enabled when
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 chip is hardware write protected,
nonvolatile writes are disabled to the Status Register,
including the Block Protect bits and the WPEN bit itself,
as well as the block-protected sections in the memory
array. Only the sections of the memory array that are not
block-protected can be written.
Note:
Since the WPEN bit is write protected, it
cannot be changed back to a “0”, as long as
the
WP
pin is held LOW.
Clock and Data Timing
Data input on the SI line is latched on the rising edge of
SCK. Data is output on the SO line by the falling edge of
SCK.
Read Sequence
When reading from the E
2
PROM memory array,
CS
is
first pulled LOW to select the device. The 8-bit READ
instruction is transmitted to the X25320, followed by the
16-bit address of which the last 12 are used. 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 ($0FFF) 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 E
2
PROM array operation sequence illustrated in
Figure 1.
XICOR [ XICOR INC. ]
