ICmic
TM
This X25020 device has been acquired by
IC MICROSYSTEMS from Xicor, Inc.
IC MICROSYSTEMS
2K
2
X25020
SPI Serial E PROM with Block Lock
TM
256 x 8 Bit
Protection
2
FEATURES
DESCRIPTION
The X25020 is a CMOS 2048-bit serial E PROM, internally
organized as 256 x 8. The X25020 features a serial
interface and software protocol allowing 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 controlled through a chip select
(CS) input, allowing any number of devices to share the
same bus.
The X25020 also features two additional inputs that
provide the end user with added flexibility. By asserting
the HOLD input, the X25020 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 X25020 disabling all write attempts, thus providing a
mechanism for limiting end user capability of altering the
memory.
The X25020 utilizes Xicor’s proprietary Direct Write™ cell,
providing a minimum endurance of 100,000 cycles
per byte and a minimum data retention of 100 years.
•
1MHz Clock Rate
•
SPI Modes (0,0 & 1,1)
•
256 X 8 Bits
—4 Byte Page Mode
•
Low Power CMOS
—10
µ
A Standby Current
—3mA Active Write 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
—Write Protect Pin
•
Self-Timed Write Cycle
—5ms Write Cycle Time (Typical)
•
High Reliability
—Endurance: 100,000 cycles per byte
—Data Retention: 100 Years
•
8-Lead PDlP Package
•
8-Lead SOIC Package
—ESD protection: 2000V on all pins
FUNCTIONAL DIAGRAM
STATUS
REGISTER
WRITE
PROTECT
LOGIC
X DECODE
LOGIC
256 BYTE
ARRAY
16
SO
SI
SCK
CS
16 X 32
COMMAND
DECODE
HOLD
AND
CONTROL
LOGIC
16
16 X 32
32
32 X 32
WP
WRITE
CONTROL
AND
TIMING
LOGIC
4
8
Y DECODE
DATA REGISTER
Direct Write
™
and Block Lock
™
Protection is a trademark of Xicor, Inc.
3834 FHD F01
Characteristics subject to change without notice
©Xicor, Inc. 1994, 1995, 1996 Patents Pending
3834-1.8 6/10/96 T3/C1/D0 NS
1
X25020
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
by the falling 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 rising edge of the serial
clock.
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 rising edge of the clock
input, while data on the SO pin change after the falling
edge of the clock input.
Chip Select (CS)
When
CS
is HIGH, the X25020 is deselected and the SO
output pin is at high impedance and unless an internal
write operation is underway, the X25020 will be in the
standby power mode.
CS
LOW enables the X25020,
placing it in the active power mode. It should be noted
that after power-up, a HIGH to LOW transition on
CS
is
required prior to the start of any operation.
Write Protect (WP)
When
WP
is LOW, nonvolatile writes to the X25020 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 X25020. If the
internal write cycle has already been initiated,
WP
going
LOW will have no affect on a write.
DIP/SOIC
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 LOW. To resume communication,
HOLD
is
brought HIGH, again while SCK is LOW. If the pause
feature is not used,
HOLD
should be held HIGH at all
times.
PIN CONFIGURATION
CS
SO
WP
VSS
1
2
3
4
X25020
8
7
6
5
VCC
HOLD
SCK
SI
3834 FHD F02.1
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
3834 PGM T01.1
2
X25020
PRINCIPLES OF OPERATION
The X25020 is a 256 x 8 E
2
PROM designed to interface
directly with the synchronous serial peripheral interface
(SPI) of many popular microcontroller families.
The X25020 contains an 8-bit instruction register. It is
accessed via the SI input, with data being clocked in on
the rising SCK.
CS
must be LOW and the
HOLD
and
WP
inputs must be HIGH during the entire operation.
Table 1 contains a list of the instructions and their
opcodes. All instructions, addresses and data are trans-
ferred MSB first.
Data input is sampled on the first rising 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 X25020 into
a “PAUSE” condition. After releasing
HOLD,
the X25020
will resume operation from the point when
HOLD
was
first asserted.
Write Enable Latch
The X25020 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
X
6
X
5
X
4
X
3
BP1
2
BP0
1
WEL
0
WIP
3834 PGM T02
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
X25020 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 X25020 is divided into four 512-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
1
1
0
1
0
1
Array Addresses
Protected
None
$C0–$FF
$80–$FF
$00–$FF
3834 PGM T03
Table 1. Instruction Set
Instruction Name
WREN
WRDI
RDSR
WRSR
READ
WRITE
Instruction Format*
0000 0110
0000 0100
0000 0101
0000 0001
0000 0011
0000 0010
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)
3834 PGM T04
*Instructions are shown MSB in leftmost position. Instructions are transferred MSB first.
3
X25020
Clock and Data Timing
Data input on the SI line is latched on the rising edge of
SCK. Data is output on the SO line by the falling edge of
SCK.
Read Sequence
When reading from the E
2
PROM memory array,
CS
is
first pulled LOW to select the device. The 8-bit READ
instruction is transmitted to the X25020, followed by the
8-bit 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 ($FF) the address counter rolls
over to address $00 allowing the read cycle to be
continued indefinitely. The read operation is termi-
nated by taking
CS
HIGH. Refer to the read E
2
PROM
array operation sequence illustrated in Figure 1.
To read the status register
CS
line is first pulled LOW
to select the device followed by the 8-bit RDSR instruc-
tion. 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 se-
quence.
Write Sequence
Prior to any attempt to write data into the X25020 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 X25020.
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.
To write data to the E
2
PROM memory array, the user
issues the WRITE instruction, followed by the address
and then the data to be written. This is minimally a thirty-
two 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 X25020. The only
restriction is that 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.
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
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 E
2
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
LOW when
HOLD
is first pulled LOW and SCK must also
be LOW when
HOLD
is released.
The HOLD input may be tied HIGH either directly to V
CC
or tied to V
CC
through a resistor.
4
X25020
Operational Notes
The X25020 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.
• SO pin is high impedance.
• The “write enable” latch is reset.
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
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
7
6
BYTE ADDRESS
5
4
3
2
1
0
DATA OUT
HIGH IMPEDANCE
SO
7
MSB
3834 FHD F04.1
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
HIGH IMPEDANCE
SO
7
MSB
6
5
4
3
2
1
0
3834 ILL F13
5
Embedded System
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