25AA080/160
transmitted, 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.
2.3
Write Status Register (WRSR)
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 below.
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 five (25AA080)
or six (25AA080) MSBs of the address being don’t care
bits, and then the data to be written. Up to 16 bytes of
data can be sent to the 25AA080/160 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 XXXX 0000 and ends with
XXXX XXXX XXXX 1111. If the internal address
counter reaches XXXX XXXX XXXX 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.
See Figure 3-6 for WRSR timing sequence.
TABLE 2-3:
ARRAY PROTECTION
Array Addresses
Write Protected
BP1
BP0
0
0
0
1
none
upper 1/4
300h-3FFh for 25AA080
600h-7FFh for 25AA160
1
1
0
1
upper 1/2
200h-3FFh for 25AA080
400h-7FFh for 25AA160
For the data to be actually written to the array, the CS
must be brought high after the least significant bit (D0)
th
of the n data byte has been clocked in. If CSis brought
all
high at any other time, the write operation will not be
completed. See Figure 3-3 and Figure 3-4 for more
detailed illustrations on the byte write sequence and the
page write sequence, respectively.
000h-3FFh for 25AA080
000h-7FFh for 25AA160
3.0
DEVICE OPERATION
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.
3.1
Clock and Data Timing
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
Read Sequence
3.4
Data Protection
The part is selected by pulling CS low. The 8-bit read
instruction is transmitted to the 25AA080/160 followed
by the 16-bit address, with the five (25AA160) or six
(25AA080) 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 ($3FF for
25AA080, $7FF for 25AA160) the address counter rolls
over to address $000 allowing the read cycle to be con-
tinued indefinitely. The read operation is terminated by
setting CS high (see Figure 3-1).
The following protection has been implemented to pre-
vent inadvertent writes to the array:
• The write enable latch is reset on power-up.
• A write enable instruction must be issued to set
the write enable latch.
• After a successful byte write, page write, or status
register write, the write enable latch is reset.
• CS must be set high after the proper number of
clock cycles to start an internal write cycle.
• Access to the array during an internal write cycle
is ignored and programming is continued.
3.5
Power On State
The 25AA080/160 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.
3.3
Write Sequence
Prior to any attempt to write data to the 25AA080/160,
the write enable latch must be set by issuing the WREN
instruction (see Figure 3-2). This is done by setting CS
low and then clocking the proper instruction into the
25AA080/160. After all eight bits of the instruction are
• A low level on CS is required to enter active state.
1996 Microchip Technology Inc.
Preliminary
DS21146D-page 7
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