25C080/160
the WREN or WRDI commands regardless of the state
of write protection on the status register.This bit is read
only.
2.0
PRINCIPLES OF OPERATION
The 25C080/160 is an 1024/2048 byte EEPROM
designed to interface directly with the Serial Peripheral
Interface (SPI) port of many of today’s popular micro-
controller families, including Microchip’s midrange
PIC16CXX microcontrollers. It may also interface with
microcontrollers that do not have a built-in SPI port by
using discrete I/O lines programmed properly with soft-
ware.
The Block Protection (BP0 and BP1) bits indicate
which blocks are currently write protected. These bits
are set by the user issuing the WRSR instruction.
These bits are non-volatile.
The Write Protect Enable (WPEN) bit is a non-volatile
bit that is available as an enable bit for the WP pin. The
Write Protect (WP) pin and the Write Protect Enable
(WPEN) bit in the status register control the program-
mable hardware write protect feature. Hardware write
protection is enabled when WP pin is low and the
WPEN bit is high. Hardware write protection is disabled
when either the WP pin is high or the WPEN bit is low.
When the chip is hardware write protected, only writes
to non-volatile bits in the status register are disabled.
See Table 2-2 for matrix of functionality on the WPEN
bit and Figure 2-1 for a flowchart of Table 2-2. See
Figure 3-5 for RDSR timing sequence.
The 25C080/160 contains an 8-bit instruction register.
The part 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. If the WPEN bit in the status register is set,
the WP pin must be held high to allow writing to the non-
volatile bits in the status register.
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 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 25C080/160 in ‘HOLD’ mode. After
releasing the HOLD pin, operation will resume from the
point when the HOLD was asserted.
TABLE 2-1:
INSTRUCTION SET
Instruction Instruction
Description
Name
Format
WREN
0000 0110 Set the write enable latch
(enable write operations)
0000 0100 Reset the write enable
latch (disable write opera-
tions)
WRDI
2.1
Write Enable (WREN) and Write
Disable (WRDI)
RDSR
WRSR
0000 0101 Read status register
0000 0001 Write status register (write
protect enable and block
write protection bits)
0000 0011 Read data from memory
array beginning at
The 25C080/160 contains a write enable latch. This
latch must be set before any write operation will be
completed internally. The WREN instruction will set the
latch, and the WRDI will reset the latch.The following is
a list of conditions under which the write enable latch
will be reset:
READ
selected address
0000 0010 Write data to memory
array beginning at
• Power-up
WRITE
• WRDI instruction successfully executed
• WRSR instruction successfully executed
• WRITE instruction successfully executed
selected address
2.2
Read Status Register (RDSR)
The RDSR instruction provides access to the status
register. The status register may be read at any time,
even during a write cycle. The status register is format-
ted as follows:
7
6
5
4
3
2
1
0
WPEN
X
X
X
BP1
BP0
WEL
WIP
The Write-In-Process (WIP) bit indicates whether the
25C080/160 is busy with a write operation.When set to
a ‘1’ a write is in progress, when set to a ‘0’ no write is
in progress. This bit is read only.
The Write Enable Latch (WEL) bit indicates the status
of the write enable latch. When set to a ‘1’ the latch
allows writes to the array and status register, when set
to a ‘0’ the latch prohibits writes to the array and status
register. The state of this bit can always be updated via
1996 Microchip Technology Inc.
Preliminary
DS21147F-page 5
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