25C320 MicrochipTechnology, 25C320 Datasheet - Page 7

• Manufacturer Part Number: 25C320
• Description: 32K5.0VSPIBusSerialEEPROM
• Manufacturer: MicrochipTechnology

2.3
The WRSR instruction allows the user to select one of
four protection options for the array by writing to the
appropriate bits in the status register. The array is
divided up into four segments. The user has the ability
to write protect none, one, two, or all four of the seg-
ments of the array. The partitioning is controlled as illus-
trated in Table 2-3.
See Figure 3-6 for WRSR timing sequence.
TABLE 2-3:
3.0
3.1
Data input on the SI pin is latched on the rising edge of
SCK. Data is output on the SO pin after the falling edge
of SCK.
3.2
The part is selected by pulling CS low. The 8-bit read
instruction is transmitted to the 25C320 followed by the
16-bit address, with the four MSBs of the address being
don’t care bits. After the correct read instruction and
address are sent, the data stored in the memory at the
selected address is shifted out on the SO pin. The data
stored in the memory at the next address can be read
sequentially by continuing to provide clock pulses. The
internal address pointer is automatically incremented to
the next higher address after each byte of data is
shifted out. When the highest address is reached
(0FFFh) the address counter rolls over to address
0000h allowing the read cycle to be continued indefi-
nitely. The read operation is terminated by setting CS
high (Figure 3-1).
3.3
Prior to any attempt to write data to the 25C320, the
write enable latch must be set by issuing the WREN
instruction (Figure 3-2). This is done by setting CS low
and then clocking the proper instruction into the
25C320. After all eight bits of the instruction are trans-
mitted, the CS must be brought high to set the write
enable latch. If the write operation is initiated
immediately after the WREN instruction without CS
being brought high, the data will not be written to the
array because the write enable latch will not have been
properly set.
1996 Microchip Technology Inc.
BP1
0
0
1
1
Write Status Register (WRSR)
DEVICE OPERATION
Clock and Data Timing
Read Sequence
Write Sequence
ARRAY PROTECTION
BP0
0
1
0
1
Array Addresses
Write Protected
0C00h - 0FFFh
0800h - 0FFFh
0000h - 0FFFh
upper 1/4
upper 1/2
none
all
Preliminary
Once the write enable latch is set, the user may pro-
ceed by setting the CS low, issuing a write instruction,
followed by the 16-bit address, with the four MSBs of
the address being don’t care bits, and then the data to
be written. Up to 32 bytes of data can be sent to the
25C320 before a write cycle is necessary. The only
restriction is that all of the bytes must reside in the
same page. A page address begins with XXXX XXXX
XXX0 0000 and ends with XXXX XXXX XXX1 1111. If
the internal address counter reaches XXXX XXXX
XXX1 1111 and the clock continues, the counter will roll
back to the first address of the page and overwrite any
data in the page that may have been written.
For the data to be actually written to the array, the CS
must be brought high after the least significant bit (D0)
of the n
high at any other time, the write operation will not be
completed. Refer to Figure 3-3 and Figure 3-4 for more
detailed illustrations on the byte write sequence and the
page write sequence respectively.
While the write is in progress, the status register may
be read to check the status of the WPEN, WIP, WEL,
BP1, and BP0 bits. A read attempt of a memory array
location will not be possible during a write cycle. When
a write cycle is completed, the write enable latch is
reset.
3.4
The following protection has been implemented to
prevent inadvertent writes to the array:
• The write enable latch is reset on power-up.
• A write enable instruction must be issued to set
• After a successful byte write, page write, or status
• CS must be set high after the proper number of
• Access to the array during an internal write cycle
3.5
The 25C320 powers on in the following state:
• The device is in low power standby mode (CS=1).
• The write enable latch is reset.
• SO is in high impedance state.
• A low level on CS is required to enter active state.
the write enable latch.
register write, the write enable latch is reset.
clock cycles to start an internal write cycle.
is ignored and programming is continued.
th
Data Protection
Power On State
data byte has been clocked in. If CS is brought
25C320
DS21159B-page 7