This X25041 device has been acquired by
IC MICROSYSTEMS from Xicor; Inc.
4K
2
X25041
SPI Serial E PROM with Block Lock
TM
512 x 8 Bit
Protection
2
FEATURES
DESCRIPTION
The X25041 is a CMOS 4096-bit serial E PROM, inter- nally
organized as 512 x 8. The X25041 features a Serial
Peripheral Interface (SPI) and software protocol allow- ing
operation on a simple three-wire bus. The bus
signals are a clock input (SCK) plus separate data in (SI)
and data out (SO) lines. Access to the device is con-
•
1MHz Clock Rate
•
SPI Modes (0,1 & 1,0)
•
512 X 8 Bits
—4 Byte Page Mode
•
Low Power CMOS
—150
∝
A Standby Current
—3mA Active Current
•
2.7V To 5.5V Power Supply
•
Block Lock Protection
2
—Protect 1/4, 1/2 or all of E PROM Array
•
Built-in Inadvertent Write Protection
—Power-Up/Power-Down protection circuitry
—Write Latch
trolled through a chip select (CS) input, allowing any
number of devices to share the same bus.
The X25041 also features two additional inputs that
provide the end user with added flexibility. By asserting
the HOLD input, the X25041 will ignore transitions on its
inputs, thus allowing the host to service higher priority
interrupts. The WP input can be used as a hardwire input to
the X25041 disabling all write attempts, thus providing
a mechanism for limiting end user capability of altering the
memory.
The X25041 utilizes Xicor’s proprietary Direct Write™ cell,
providing a minimum endurance of 100,000 cycles
—Write Protect
Pin
•
Self-Timed Write Cycle
—5ms Write Cycle Time (Typical)
•
High Reliability
—Endurance: 100,000 cycles per byte
—Data Retention: 100 Years
—ESD protection: 2000V on all pins
•
8-Lead PDlP Package
•
8-Lead SOIC Package
per byte and a minimum data retention of 100 years.
FUNCTIONAL DIAGRAM
STATUS
REGISTER
WRITE
PROTECT
LOGIC
X DECODE
LOGIC
512 BYTE
ARRAY
32
32 X 32
SO
SI
COMMAND
DECODE
SCK
CS
HOLD
AND
CONTROL
LOGIC
32
32 X 32
64
64 X 32
WP
WRITE
CONTROL
AND
TIMING
LOGIC
4
8
Y DECODE
DATA REGISTER
6556 FHD F01
Direct Write™ and Block Lock™ Protection is a trademark of Xicor, Inc.
©Xicor, Inc. 1995, 1996 Patents Pending
6556-1.2 6/10/96 T6/C1/D0 NS
1
Characteristics subject to change without notice
X25041
PIN DESCRIPTIONS
Serial Output (SO)
SO is a push/pull serial data output pin. During a read
cycle, data is shifted out on this pin. Data is clocked out
Hold (HOLD)
HOLD is used in conjunction with the CS pin to select the
device. Once the part is selected and a serial sequence is
underway, HOLD may be used to pause the serial
communication with the controller without resetting the
serial sequence. To pause, HOLD must be brought LOW
while SCK is HIGH. To resume communication, HOLD is
by the rising edge of the serial clock.
Serial Input (SI)
SI is the serial data input pin. All opcodes, byte ad-
dresses, and data to be written to the memory are input
on this pin. Data is latched by the falling edge of the serial
clock.
brought HIGH, again while SCK is HIGH. If the pause
feature is not used, HOLD should be held HIGH at all
times.
PIN CONFIGURATION
DIP/SOIC
1
2
3
4
X25041
8
7
6
5
V
CC
HOLD
SCK
Serial Clock (SCK)
The Serial Clock controls the serial bus timing for data
input and output. Opcodes, addresses, or data present
on the SI pin are latched on the falling edge of the clock
input, while data on the SO pin change after the rising
CS
SO
edge of the clock input.
Chip Select (CS)
When CS is HIGH, the X25041 is deselected and the SO
output pin is at high impedance and unless an internal
WP
V
SS
SI
6556 FHD F02
write operation is underway, the X25041 will be in the
standby power mode. CS LOW enables the X25041,
placing it in the active power mode. It should be noted that
after power-up, a HIGH to LOW transition on CS is
PIN NAMES
Symbol
CS
SO
SI
SCK
WP
V
SS
V
CC
HOLD
Description
Chip Select Input
Serial Output
Serial Input
Serial Clock Input
Write Protect Input
Ground
Supply Voltage
Hold Input
6556 PGM T01
required prior to the start of any operation.
Write Protect (WP)
When WP is LOW, nonvolatile writes to the X25041 are
disabled, but the part otherwise functions normally.
When WP is held HIGH, all functions, including nonvola- tile
writes operate normally. WP going LOW while CS is
still LOW will interrupt a write to the X25041. If the
internal write cycle has already been initiated, WP going
LOW will have no affect on a write.
2
X25041
PRINCIPLES OF OPERATION
The X25041 is a 512 x 8 E PROM designed to interface
directly with the synchronous serial peripheral interface
2
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:
(SPI) of many popular microcontroller families.
The X25041 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
7
X
6
X
5
X
4
X
3
BP1
2
BP0
1
WEL
0
WIP
6556 PGM T02
BP0 and BP1 are set by the WRSR instruction. WEL
and WIP are read-only and automatically set by other
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
X25041 into a “PAUSE” condition. After releasing HOLD,
the X25041 will resume operation from the point when
HOLD was first asserted.
operations.
The Write-In-Process (WIP) bit indicates whether the
X25041 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 X25041 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.
Write Enable Latch
The X25041 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
The partitioning is controlled as illustrated below.
Status Register Bits
BP1
BP0
0
0
1
1
0
1
0
1
Array Addresses
Protected
None
$180–
$1FF
$100–
$1FF
$000–
$1FF
6556 PGM T03
cycle.
Table 1. Instruction Set
Instruction Name
WREN
WRDI
RDSR
WRSR
READ
WRITE
Instruction Format*
0000 0110
0000 0100
0000 0101
0000 0001
0000 A
8
011
0000 A
8
010
Operation
Set the Write Enable Latch (Enable Write Operations)
Reset the Write Enable Latch (Disable Write Operations)
Read Status Register
Write Status Register
Read Data from Memory Array beginning at selected address
Write Data to Memory Array beginning at Selected Address (1
to 32 Bytes)
6556 PGM T04
*Instructions are shown MSB in leftmost position. Instructions are transferred MSB first.
3
X25041
Clock and Data Timing
Data input on the SI line is latched on the falling edge of
SCK. Data is output on the SO line by the rising edge of
For the write operation (byte or page write) to be
completed, CS can only be brought HIGH after bit 0 of
data byte N is clocked in. If it is brought HIGH at any other
time the write operation will not be completed. Refer to
SCK.
Read Sequence
2
When reading from the E PROM memory array, CS is first
pulled LOW to select the device. The 8-bit READ
instruction is transmitted to the X25041, followed by the 8-
bit address. Bit 3 of the Read Data instruction con-
tains address A
8
. This bit is used to select the upper or
lower half of the address. After the READ opcode and
address are sent, the data stored in the memory at the
selected address is shifted out on the SO line. The data
stored in memory at the next address can be read
sequentially by continuing to provide clock pulses. The
address is automatically incremented to the next higher
address after each byte of data is shifted out. When the
highest address is reached ($1FF) the address counter
rolls over to address $000 allowing the read cycle to be
Figures 4 and 5 below for a detailed illustration of the write
sequences and time frames in which CS going
HIGH are valid.
To write to the status register, the WRSR instruction is
followed by the data to be written. Data bits 0, 1, 4, 5, 6
and 7 must be “0”. Figure 6 illustrates this sequence.
While the write is in progress following a status register or
2
E PROM write sequence, the status register may be
read to check the WIP bit. During this time the WIP bit will be
HIGH.
Hold Operation
The HOLD input should be HIGH (at V
IH
) under normal
operation. If a data transfer is to be interrupted HOLD
can be pulled LOW to suspend the transfer until it can be
resumed. The only restriction is the SCK input must be
continued indefinitely. The read operation is termi-
2
nated by taking CS HIGH. Refer to the read E PROM
array operation sequence illustrated in Figure 1.
To read the status register, the CS line is first pulled
LOW to select the device followed by the 8-bit RDSR
instruction. After the read status register opcode is
sent, the contents of the status register are shifted out
on the SO line. Figure 2 illustrates the read status
register sequence.
Write Sequence
Prior to any attempt to write data into the X25041, the
“write enable” latch must first be set by issuing the
WREN instruction (See Figure 3). CS is first taken LOW,
then the WREN instruction is clocked into the X25041.
After all eight bits of the instruction are transmitted, CS
must then be taken HIGH. If the user continues the write
operation without taking CS HIGH after issuing the
WREN instruction, the write operation will be ignored.
HIGH when HOLD is first pulled LOW and SCK must
also be HIGH when HOLD is released.
The HOLD input may be tied HIGH either directly to V
CC
or
tied to V
CC
through a resistor.
To write data to the E PROM memory array, the user
issues the WRITE instruction, followed by the address
and then the data to be written. This is minimally a
twenty-four clock operation. CS must go LOW and
remain LOW for the duration of the operation. The host may
continue to write up to 4 bytes of data to the X25041.
2
The only restriction is the 4 bytes must reside on the
same page. If the address counter reaches the end of
the page and the clock continues, the counter will “roll
over” to the first address of the page and overwrite any
data that may have been written.
4
X25041
Operational Notes
The X25041 powers-up in the following state:
•The device is in the low power standby state.
•A HIGH to LOW transition on CS is required to
enter an active state and receive an instruction.
Data Protection
The following circuitry has been included to prevent
inadvertent writes:
•The “write enable” latch is reset upon power-up. •A
WREN instruction must be issued to set the “write
enable” latch.
•CS must come HIGH at the proper clock count in
•SO pin is high impedance. •The
“write enable” latch is reset.
order to start a write cycle.
Figure 1. Read E
2
PROM Array Operation Sequence
CS
0
SCK
1
2
3
4
5
6
7
8
9
10 11 12 13 14 15 16 17 18 19 20 21 22
INSTRUCTION
SI
8
7
6
BYTE ADDRESS
5
4
3
2
1
0
9TH BIT OF ADDRESS
DATA OUT
SO
HIGH IMPEDANCE
7
MSB
6556 FHD F14.1
6
5
4
3
2
1
0
Figure 2. Read Status Register Operation Sequence
CS
0
SCK
1
2
3
4
5
6
7
8
9
10 11 12 13 14
INSTRUCTION
SI
DATA OUT
SO
HIGH IMPEDANCE
7
MSB
6
5
4
3
2
1
0
6556 ILL F13
5
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