25AA160/25LC160/25C160
3.3
Write Sequence
3.0
3.1
FUNCTIONAL DESCRIPTION
Principles of Operation
Prior to any attempt to write data to the 25XX160, the
write enable latch must be set by issuing the WREN
instruction (Figure 3-4). This is done by setting CS low
and then clocking out the proper instruction into the
25XX160. 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 immedi-
ately 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.
The 25XX160 are 2048 byte Serial EEPROMs
designed to interface directly with the Serial Peripheral
Interface (SPI) port of many of today’s popular micro-
controller families, including Microchip’s PIC16C6X/7X
microcontrollers. It may also interface with microcon-
trollers that do not have a built-in SPI port by using dis-
crete I/O lines programmed properly with the software.
The 25XX160 contains an 8-bit instruction register. The
device is accessed via the SI pin, with data being
clocked in on the rising edge of SCK. The CS pin must
be low and the HOLD pin must be high for the entire
operation. The WP pin must be held high to allow
writing to the memory array.
Once the write enable latch is set, the user may
proceed by setting the CS low, issuing a WRITEinstruc-
tion, followed by the 16-bit address, with the five 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
25XX160 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 xxxxxxxx
xxxx0000and ends with xxxxxxxxxxxx1111.
If the internal address counter reaches xxxx xxxx
xxxx1111and 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.
Table 3-1 contains a list of the possible instruction
bytes and format for device operation. All instructions,
addresses, and data are transferred MSB first, LSB
last.
Data is sampled on the first rising edge of SCK after CS
goes low. If the clock line is shared with other periph-
eral devices on the SPI bus, the user can assert the
HOLD input and place the 25XX160 in ‘HOLD’ mode.
After releasing the HOLD pin, operation will resume
from the point when the HOLD was asserted.
For the data to be actually written to the array, the CS
must be brought high after the Least Significant bit (D0)
of the nth data byte has been clocked in. If CS is
brought high at any other time, the write operation will
not be completed. Refer to Figure 3-2 and Figure 3-3
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 (Figure 3-6). A read attempt of a
memory array location will not be possible during a
write cycle. When the write cycle is completed, the
write enable latch is reset.
3.2
Read Sequence
The device is selected by pulling CS low. The 8-bit
READ instruction is transmitted to the 25XX160
followed by the 16-bit address, with the five MSBs of
the address being "don’t care" bits. After the correct
READinstruction 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 (07FFh), the address counter rolls
over to address 0000h allowing the read cycle to be
continued indefinitely. The read operation is terminated
by raising the CS pin (Figure 3-1).
TABLE 3-1:
INSTRUCTION SET
Instruction Name
Instruction Format
Description
READ
WRITE
WRDI
WREN
RDSR
WRSR
0000 0011
0000 0010
0000 0100
0000 0110
0000 0101
0000 0001
Read data from memory array beginning at selected address
Write data to memory array beginning at selected address
Reset the write enable latch (disable write operations)
Set the write enable latch (enable write operations)
Read Status register
Write Status register
1997-2012 Microchip Technology Inc.
DS21231E-page 7
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