25LC040A-I/SN Microchip Technology, 25LC040A-I/SN Datasheet - Page 6

• Manufacturer Part Number: 25LC040A-I/SN
• Description: IC EEPROM 4KBIT 10MHZ 8SOIC
• Manufacturer: Microchip Technology

Specifications of 25LC040A-I/SN

• Memory Size: 4K (512 x 8)
• Format - Memory: EEPROMs - Serial
• Memory Type: EEPROM
• Speed: 10MHz
• Interface: SPI, 3-Wire Serial
• Voltage - Supply: 2.5 V ~ 5.5 V
• Operating Temperature: -40°C ~ 85°C
• Package / Case: 8-SOIC (3.9mm Width)
• Memory Configuration: 512 X 8 / 256 X 16
• Ic Interface Type: SPI
• Clock Frequency: 10MHz
• Supply Voltage Range: 2.5V To 5.5V
• Memory Case Style: SOIC
• No. Of Pins: 8
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

25AA040A/25LC040A
2.0
2.1
The 25XX040A is a 512-byte Serial EEPROM
designed to interface directly with the Serial Peripheral
Interface (SPI) port of many of today’s popular
microcontroller families, including Microchip’s PIC
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 in firmware to
match the SPI protocol.
The 25XX040A 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.
Table 2-1 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 (SI) is sampled on the first rising edge of SCK
after CS goes low. If the clock line is shared with other
peripheral devices on the SPI bus, the user can assert
the HOLD input and place the 25XX040A in ‘HOLD’
mode. After releasing the HOLD pin, operation will
resume from the point when the HOLD was asserted.
2.2
The device is selected by pulling CS low. The 8-bit
READ instruction is transmitted to the 25XX040A
followed by a 9-bit address. The MSb (A8) is sent to the
slave during the instruction sequence. See Figure 2-1
for more details.
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. Data stored in the memory
at the next address can be read sequentially by
continuing to provide clock pulses to the slave. 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
(1FFh), the address counter rolls over to address 000h
allowing the read cycle to be continued indefinitely. The
read operation is terminated by raising the CS pin
(Figure 2-1).
2.3
Prior to any attempt to write data to the 25XX040A, the
write enable latch must be set by issuing the WREN
instruction (Figure 2-4). This is done by setting CS low
and then clocking out the proper instruction into the
25XX040A. After all eight bits of the instruction are
transmitted, CS must be driven high to set the write
enable latch.
DS21827F-page 6
FUNCTIONAL DESCRIPTION
Principles of Operation
Read Sequence
Write Sequence
®
If the write operation is initiated immediately after the
WREN instruction without CS driven high, data will not
be written to the array since the write enable latch was
not properly set.
After setting the write enable latch, the user may
proceed by driving CS low, issuing a WRITE instruction,
followed by the remainder of the address, and then the
data to be written. Keep in mind that the Most
Significant address bit (A8) is included in the instruction
byte for the 25XX040A. Up to 16 bytes of data can be
sent to the device before a write cycle is necessary.
The only restriction is that all of the bytes must reside
in the same page. Additionally, a page address begins
with ‘XXXX 0000’ and ends with ‘XXXX 1111’. If the
internal address counter reaches ‘XXXX 1111’ and
clock signals continue to be applied to the chip, the
address counter will roll back to the first address of the
page and over-write any data that previously existed in
those locations.
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 2-2 and Figure 2-3 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 2-6). Attempting to read a memory
array location will not be possible during a write cycle.
Polling the WIP bit in the STATUS register is recom-
mended in order to determine if a write cycle is in prog-
ress. When the write cycle is completed, the write
enable latch is reset.
Note:
th
data byte has been clocked in. If CS is driven
Page write operations are limited to writing
bytes within a single physical page,
regardless of the number of bytes
actually being written. Physical page
boundaries start at addresses that are
integer multiples of the page buffer size (or
‘page size’) and, end at addresses that are
integer multiples of page size – 1. If a
Page Write command attempts to write
across a physical page boundary, the
result is that the data wraps around to the
beginning of the current page (overwriting
data previously stored there), instead of
being written to the next page as might be
expected. It is therefore necessary for the
application software to prevent page write
operations that would attempt to cross a
page boundary.
© 2009 Microchip Technology Inc.