X25021 Datasheet, PDF (3/14 Pages) Xicor Inc. – SPI Serial E2PROM with Block LockTM Protection

X25021
PRINCIPLES OF OPERATION
The X25021 is a 256 x 8 E²PROM designed to interface
directly with the synchronous serial peripheral interface
(SPI) of many popular microcontroller families.
The X25021 contains an 8-bit instruction register. It is
accessed via the SI input, with data being clocked in on
the falling SCK. CS must be LOW during the entire
operation.
Table 1 contains a list of the instructions and their codes.
All instructions, addresses and data are transferred
MSB first.
Data input is sampled on the first falling edge of SCK
after CS goes LOW. SCK is static, allowing the user to
stop the clock and then resume operations. If the clock
line is shared with other peripheral devices on the SPI
bus, the user can assert the HOLD input to place the
X25021 into a “PAUSE” condition. After releasing HOLD,
the X25021 will resume operation from the point when
HOLD was first asserted.
Write Enable Latch
The X25021 contains a “write enable” latch. This latch
must be SET before a write operation will be completed
internally. The WREN instruction will set the latch and
the WRDI instruction will reset the latch. This latch is
automatically reset upon a power-up condition and after
the completion of a byte, page, or status register write
cycle.
Status Register
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:
7 654 3
2
1
0
X X X X BP1 BP0 WEL WIP
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BP0 and BP1 are set by the WRSR instruction. WEL
and WIP are read-only and automatically set by other
operations.
The Write-In-Process (WIP) bit indicates whether the
X25021 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. During a write, all other bits are set to “1”.
The Write Enable Latch (WEL) bit indicates the status of
the “write enable” latch. When set to a “1”, the latch is set,
when set to a “0”, the latch is reset.
The Block Protect (BP0 and BP1) bits are nonvolatile
and allow the user to select one of four levels of protec-
tion. The X25021 is divided into four 1024-bit segments.
One, two, or all four of the segments may be protected.
That is, the user may read the segments but will be
unable to alter (write) data within the selected segments.
The partitioning is controlled as illustrated below.
Status Register Bits
BP1
BP0
0
0
0
1
1
0
1
1
Array Addresses
Protected
None
$C0–$FF
$80–$FF
$00–$FF
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Table 1. Instruction Set
Instruction Name Instruction Format*
Operation
WREN
0000 0110
Set the Write Enable Latch (Enable Write Operations)
WRDI
0000 0100
Reset the Write Enable Latch (Disable Write Operations)
RDSR
0000 0101
Read Status Register
WRSR
0000 0001
Write Status Register
READ
0000 0011
Read Data from Memory Array beginning at selected address
WRITE
0000 0010
Write Data to Memory Array beginning at Selected Address
(1 to 32 Bytes)
*Instructions are shown MSB in leftmost position. Instructions are transferred MSB first.
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