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APPLICATION NOTE
A V A I LABLE
AN61 • AN75 • AN77 • AN79 • AN82
X25F064/032/016/008
SerialFlash™ Memory With Block LockTM Protection
FEATURES
• 1MHz Clock Rate
• SPI Serial Interface
• 64K/32K/16K/8K Bits
— 32 Byte Small Sector Program Mode
• Low Power CMOS
— <1µA Standby Current
— <5mA Active Current
• 1.8V – 3.6V or 5V “Univolt” Read and
Program Power Supply Versions
• Block Lock Protection
— Protect 1/4, 1/2, or all of E2PROM Array
• Built-in Inadvertent Program Protection
— Power-Up/Power-Down protection circuitry
— Program Enable Latch
— Program Protect Pin
• Self-Timed Program Cycle
— 5ms Program 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 150 mil SOIC Packages
• 32K, 16K, 8K available in 14-Lead TSSOP,
64K available in 20-Lead TSSOP
DESCRIPTION
The X25F064/032/016/008 family are 8/16/32/64K-bit
CMOS SerialFlash memory, internally organized
X 8. They feature a “Univolt” Program and Read voltage,
Serial Peripheral Interface (SPI), 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 X25F064/032/016/008 also features two additional
inputs that provide the end user with added flexibility. By
asserting the HOLD input, the X25F064/032/016/008
will ignore transitions on its inputs, thus allowing the host
to service higher priority interrupts. The PP input can be
used as a hardwire input to the X25F064/032/016/008
disabling all program attempts to the status register,
thus providing a mechanism for limiting end user capa-
bility of altering 0, 1/4, 1/2, or all of the memory.
The X25F064/032/016/008 utilizes Xicor’s proprietary
flash cell, providing a minimum endurance
of 100,000 cycles and a minimum data retention of
100 years.
FUNCTIONAL DIAGRAM
SI
SO
SCK
COMMAND
DECODE
AND CONTROL
LOGIC
X
DECODE
LOGIC
DATA REGISTER
SECTOR DECODE LOGIC
32 8
MEMORY
ARRAY
CS
HOLD
STATUS
REGISTER
PP
PROGRAMMING
CONTROL LOGIC
SerialFlash™ and Block Lock™ Protection are trademarks of Xicor, Inc.
© Xicor, Inc. 1995, 1996 Patents Pending
6685-3.1 8/29/96 T3/C0/D0 SH
HIGH VOLTAGE
CONTROL
6685 ILL F01.4
Characteristics subject to change without notice

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X25F064/032/016/008
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
addresses, 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 X25F064/032/016/008 is
deselected and the SO output pin is at high impedance
and unless an internal program operation is underway
the X25F064/032/016/008 will be in the standby power
mode. CS LOW enables the X25F064/032/016/008,
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.
Program Protect (PP)
When PP is LOW and the nonvolatile bit PPEN is “1”,
nonvolatile programming of the X25F064/032/016/008
status register is disabled, but the part otherwise func-
tions normally. When PP is held HIGH, all functions,
including nonvolatile programming operate normally.
PP going LOW while CS is still LOW will interrupt
programming of the X25F064/032/016/008 status regis-
ter. If the internal program cycle has already been
initiated, PP going LOW will have no effect on program-
ming.
The PP pin function is blocked when the PPEN bit in
the status register is “0”. This allows the user to install the
X25F064/032/016/008 into a system with PP pin
grounded and still be able to program the status register.
The PP pin functions will be enabled when the PPEN bit
is set “0”.
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
PP
VSS
8-Lead DIP/SOIC
18
2 X25F064/ 7
3
032/016/
008
6
45
VCC
HOLD
SCK
SI
CS
SO
NC
NC
NC
PP
VSS
14-Lead TSSOP
1 14
2 13
3 12
X25F032/
4 016/008 11
5 10
69
78
VCC
HOLD
NC
NC
NC
SCK
SI
NC
CS
NC
SO
NC
NC
PP
VSS
NC
NC
20-Lead TSSOP
1 20
2 19
3 18
4 17
5 X25F064 16
6 15
7 14
8 13
9 12
10 11
NC
VCC
NC
HOLD
NC
NC
SCK
SI
NC
NC
6685 ILL F02.4
PIN NAMES
SYMBOL
CS
SO
SI
SCK
PP
VSS
VCC
HOLD
NC
DESCRIPTION
Chip Select Input
Serial Output
Serial Input
Serial Clock Input
Program Protect Input
Ground
Supply Voltage
Hold Input
No Connect
6685 PGM T01.1
2

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X25F064/032/016/008
PRINCIPLES OF OPERATION
formatted as follows:
The X25F064/032/016/008 family are SerialFlash
Memory designed to interface directly with the synchro-
nous serial peripheral interface (SPI) of many popular
microcontroller families.
The X25F064/032/016/008 family 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 PP inputs must be HIGH during
the entire operation. The PP input is “Don’t Care” if
PPEN is set “0”.
Table 1 contains a list of the instructions and their
operation codes. All instructions, addresses and data
are transferred 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 X25F064/
032/016/008 into a “PAUSE” condition. After
releasing HOLD, the X25F064/032/016/008 device will
resume operation from the point when HOLD was first
asserted.
Program Enable Latch
The X25F064/032/016/008 device contains a
program enable latch. This latch must be SET before a
program operation will be completed internally. The
PREN instruction will set the latch and the PRDI
instruction will reset the latch. This latch is automatically
reset on power-up and after the completion of a sector
program 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 program cycle. The status register is
Table 1. Instruction Set
7 654 3
2 10
PPEN X X X BL1 BL0 PEL PIP
6685 PGM T02.2
PPEN, BL0, and BL1 are set by the PRSR instruction.
PEL and PIP are “read-only” and automatically set by
other operations.
The Programming-In-Process (PIP) bit indicates
whether the X25F064/032/016/008 device is busy
with a program operation. When set to a “1”
programming is in progress, when set to a “0” no
programming is in progress. During programming, all
other bits are set to “1”.
The Program Enable Latch (PEL) bit indicates the
status of the program enable latch. When set to a “1” the
latch is set; when set to a “0” the latch is reset.
The Block Lock (BL0 and BL1) bits are nonvolatile and
allow the user to select one of four levels of protection.
The X25F064/032/016/008 device array is divided into
four equal segments. One, two, or all four of the seg-
ments may be locked. That is, the user may read the
segments, but will be unable to alter (program) data
within the selected segments. The partitioning is con-
trolled as illustrated below.
Status Register Bits
BL1 BL0
Array Addresses
Locked
00
01
10
11
Program-Protect Enable
None
upper fourth
upper half
All
6685 PGM T03.1
The Program-Protect-Enable bit (PPEN) in the
X25F064/032/016/008 status register acts as an
enable bit for the PP pin.
Instruction Name Instruction Format*
Operation
PREN
0000 0110
Set the Program Enable Latch (Enable Program Operations)
PRDI
0000 0100
Reset the Program Enable Latch (Disable Program Operations)
RDSR
0000 0101
Read Status Register
PRSR
0000 0001
Program Status Register
READ
0000 0011
Read from Memory Array beginning at Selected Address
PROGRAM
0000 0010
Program Memory Array beginning at Selected Address
(32 Bytes)
*Instructions are shown MSB in leftmost position. Instructions are transferred MSB first.
6685 PGM T04.2
3

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X25F064/032/016/008
Locked Unlocked
PPEN PP PEL Blocks Blocks
Status
Register
0 X 0 Locked Locked
Locked
0 X 1 Locked Programmable Programmable
1 LOW 0 Locked Locked
Locked
1 LOW 1 Locked Programmable Locked
X HIGH 0 Locked Locked
Locked
X HIGH 1 Locked Programmable Programmable
6685 PGM T05.2
The Program Protect (PP) pin and the nonvolatile
Program Protect Enable (PPEN) bit in the Status Reg-
ister control the programmable hardware write protect
feature. Hardware program protection is enabled when
PP pin is LOW, and the PPEN bit is “1”. Hardware
program protection is disabled when either the PP pin is
HIGH or the PPEN bit is “0”. When the chip is hardware
program protected, nonvolatile programming of the Sta-
tus Register in disabled, including the Block Lock bits
and the PPEN bit itself, as well as the Block Lock
sections in the memory array. Only the sections of the
memory array that are not Block Locked can be pro-
grammed.
Note: Since the PPEN bit is program protected, it
cannot be changed back to a “0”, as long as
the PP pin is held LOW.
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 SerialFlash memory array, CS is
first pulled LOW to select the device. The 8-bit READ
instruction is transmitted to the X25F064/032/016/008
device, followed by the 16-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 the address
counter rolls over to address $0000, allowing the read
cycle to be continued indefinitely. The read operation is
terminated by taking CS HIGH. Refer to the Read
SerialFlash Memory 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 instruc-
tion. After the read status register opcode is sent, the
contents of the status register are shifted out on the SO
line. The Read Status Register Sequence is illustrated
in Figure 2.
Programming Sequence
Prior to any attempt to program the X25F064/032/016/
008 device, the program enable latch must first be set by
issuing the PREN instruction (See Figure 3). CS is first
taken LOW, then the PREN instruction is clocked into
the X25F064/032/016/008 device. After all eight bits of
the instruction are transmitted, CS must then be taken
HIGH. If the user continues the programming operation
without taking CS HIGH after issuing the PREN instruc-
tion, the programming operation will be ignored.
To program the SerialFlash memory array, the user
issues the PROGRAM instruction, followed by the ad-
dress of the first location in the sector and then the data
to be programmed. The data is programmed in a 256-
clock operation. CS must go LOW and remain LOW for
the duration of the operation. The 32 bytes must reside
in the same sector and cannot cross sector boundaries.
If the address counter reaches the end of the sector
and the clock continues, or if fewer than 32 bytes are
clocked in, the contents of the sector cannot be guaranteed.
For the program operation to be completed, CS can only
be brought HIGH after bit 0 of data byte 32 is clocked in.
If it is brought HIGH at any other time the program
operation will not be completed. Refer to Figure 4 below
for a detailed illustration of the programming sequence
and time frames in which CS going HIGH is valid.
To program the status register, the PRSR instruction is
followed by the data to be programmed. Data bits 0, 1,
4, 5 and 6 must be “0”. This sequence is shown in Figure 5.
While the program cycle is in progress, following a
status register or memory write sequence, the status
register may be read to check the PIP bit. During this
time the PIP bit will be HIGH.
Hold Operation
The HOLD input should be HIGH (at VIH) 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 that 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 VCC
or tied to VCC through a resistor.
4

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X25F064/032/016/008
Operational Notes
The device 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 program enable latch is reset.
Data Protection
The following circuitry has been included to prevent
inadvertent programming:
• The program enable latch is reset upon power-up.
• A program enable instruction must be issued to set
the program enable latch.
CS must come HIGH at the proper clock count in
order to start a program cycle.
Figure 1. Read SerialFlash Memory Array Operation Sequence
CS
SCK
0 1 2 3 4 5 6 7 8 9 10
20 21 22 23 24 25 26 27 28 29 30
INSTRUCTION
16 BIT ADDRESS
SI
15 14 13
3210
HIGH IMPEDANCE
SO
76
MSB
DATA OUT
543210
6685 ILL F03
Figure 2. Read Status Register Operation Sequence
CS
SCK
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14
INSTRUCTION
SI
HIGH IMPEDANCE
SO
76
MSB
DATA OUT
543210
6685 ILL F04
5