notice. ISSI products are not designed, intended, authorized or warranted for use as components in systems or equipment intended for critical medical or surgical equip-
ment, aerospace systems, or for other applications planned to support or sustain life. It is the customer's obligation to optimize the design in their own products for the best
performance and optimization on the functionality and etc. ISSI assumes no liability arising out of the application or use of any information, products or services described
herein. Customers are advised to obtain the latest version of this device specification before relying on any published information and prior placing orders for products.
Integrated Silicon Solution, Inc.
Preliminary Information
08/25/09
Rev. 00A
1
IS25C08B
PIN CONFIGURATION
8-Pin SOIC and TSSOP
8-pad UDFN
CS
SO
WP
GND
1
2
3
4
8
7
6
5
VCC
HOLD
SCK
SI
CS
1
SO 2
WP
3
GND 4
8 VCC
7
HOLD
6 SCK
5 SI
(Top View)
PIN DESCRIPTIONS
CS
SCK
SI
SO
GND
V
cc
WP
HOLD
Chip Select
Serial Data Clock
Serial Data Input
Serial Data Output
Ground
Power
Write Protect
Suspends Serial Input
Chip Select (CS):
The
CS
pin activates the device.
Upon power-up,
CS
should follow Vcc. When the de-
vice is to be enabled for instruction input, the signal re-
quires a High-to-Low transition. While
CS
is stable Low,
the master and slave will communicate via SCK, SI, and
SO signals. Upon completion of communication,
CS
must be driven High. At this moment, the slave device
may start its internal write cycle. When
CS
is high, the
device enters a power-saving standby mode, unless an
internal write operation is underway. During this mode,
the SO pin becomes high impedance.
Write Protect (WP):
The purpose of this input signal is
to initiate Hardware Write Protection mode. This mode
prevents the Block Protection bits and the WPEN bit in
the Status Register from being altered. To cause Hard-
ware Write Protection,
WP
must be Low at the same
time WPEN is 1.
WP
may be hardwired to Vcc or GND.
HOLD (HOLD):
This input signal is used to suspend
the device in the middle of a serial sequence and tem-
porarily ignore further communication on the bus (SI,
SO, SCK). Together with Chip Select, the
HOLD
signal
allows multiple slaves to share the bus. The
HOLD
signal transitions must occur only when SCK is Low,
and be held stable during SCK transitions. (See Figure
8 for Hold timing) To disable this feature,
HOLD
may be
hardwired to Vcc.
PIN DESCRIPTIONS
Serial Clock (SCK):
This timing signal provides
synchronization between the microcontroller and
IS25C08B. Op-Codes, byte addresses, and data are
latched on SI with a rising edge of the SCK. Data on
SO is refreshed on the falling edge of SCK for SPI
modes (0,0) and (1,1).
Serial Data Input (SI):
This is the input pin for all data
that the IS25C08B is required to receive.
Serial Data Output (SO):
This is the output pin for all
data transmitted from the IS25C08B.
2
Integrated Silicon Solution, Inc.
Preliminary Information Rev. 00A
08/25/09
IS25C08B
SERIAL INTERFACE DESCRIPTION
MASTER:
The device that provides a clock signal.
SLAVE:
The IS25C08B is a slave because the clock
signal is an input.
TRANSMITTER/RECEIVER:
The IS25C08B has both
data input (SI) and data output (SO).
MSB:
The most significant bit. It is always the first bit
transmitted or received.
OP-CODE:
The first byte transmitted to the slave fol-
lowing CS transition to LOW. If the OP-CODE is a valid
member of the IS25C08B instruction set (Table 3), then
it is decoded appropriately. If the OP-CODE is not valid,
and the SO pin remains in high impedance.
BLOCK DIAgRAM
VCC
GND
STATUS
REGISTER
1024 x 8
MEMORY ARRAY
DATA
REGISTER
SI
MODE
DECODE
LOGIC
ADDRESS
DECODER
OUTPUT
BUFFER
CS
WP
SCK
CLOCK
SO
HOLD
Integrated Silicon Solution, Inc.
Preliminary Information
08/25/09
Rev. 00A
3
IS25C08B
The status register contains 8-bits for write protection
control and write status. (See Table 1). It is the only
region of memory other than the main array that is ac-
cessible by the user.
STATUS REgISTER
Table 1. Status Register Format
Bit 7
Bit 6 Bit 5 Bit 4
X
X
Bit 3 Bit 2 Bit1 Bit 0
BP1 BP0 WEN
RDY
WPEN X
Block Protect (BP1, BP0), Bits 2-3:
Together, these
bits represent one of four block protection configura-
tions implemented for the memory array. (See Table 2
for details.)
BP0 and BP1 are non-volatile cells similar to regular
array cells, and factory programmed to 0. The block
of memory defined by these bits is always protected,
regardless of the setting of WPEN,
WP
, or WEN.
Notes:
1. X =
Don't care bit.
2. During internal write cycles, bits 0 to 7 are temporarily 1's.
Table 2. Block Protection
Status
Register
Bits
Level
0
1(1/4)
2(1/2)
3(All)
BP1
0
0
1
1
BP0
0
1
0
1
Array Addresses Protected
IS25C08B
None
0300h
-03FFh
0200h
-03FFh
0000h
-03FFh
The Status Register is Read-Only if either: a) Hardware
Write Protection is enabled or b) WEN is set to 0. If
neither is true, it can be modified by a valid instruction.
Ready (RDY), Bit 0:
When
RDY
= 1, it indicates that
the device is busy with a write cycle.
RDY
= 0 indicates
that the device is ready for an instruction. If
RDY
= 1,
the only command that will be handled by the device is
Read Status Register.
Write Enable (WEN), Bit 1:
This bit represents the
status of device write protection. If WEN = 0, the Status
Register and the entire array is protected from modifi-
cation, regardless of the setting of WPEN,
WP
pin, or
block protection. The only way to set WEN to 1 is via
the Write Enable command (WREN). WEN is reset to 0
upon power-up.
Don’t Care, Bits 4-6:
Each of these bits can receive ei-
ther 0 or 1, but values will not be retained. When these
bits are read from the register, they are always 0.
Write Protect Enable (WPEN), Bit 7:
This bit can be
used in conjunction with
WP
pin to enable Hardware
Write Protection, which causes the Status Register to
be read-only. The memory array is not protected by this
mode. Hardware Write Protection requires that
WP
= 0
and
WPEN = 1; it is disabled otherwise. Note: WPEN
cannot be changed from 1 to 0 if the
WP
pin is already
set to Low. (See Table 4 for data protection relation-
ship)
4
Integrated Silicon Solution, Inc.
Preliminary Information Rev. 00A
08/25/09
IS25C08B
DEVICE OPERATION
T
he operations of the IS25C08B are controlled by a set of instructions that are clocked-in serially SI pin. (See Table
3). To begin an instruction, the chip select (CS) should be dropped Low. Subsequently, each Low-to-High transition
of the clock (SK) will latch a stable value on the SI pin. After the 8-bit op-code, it may be appropriate to continue to
input an address or data to SI, or to output data from SO. During data output, values appear on the falling edge of
SK. All bits are transferred with MSB first. Upon the last bit of communication, but prior to any following Low-to-High
transition of SK,
CS
should be raised High to end the transaction. The device then would enter Standby Mode if no
internal programming were underway.
Table 3. Instruction Set
Name
WRDI
RDSR
WRSR
READ
WRITE
Op-code
0000 X100
0000 X101
0000 X001
0000 X011
0000 X010
Operation
Set Write Enable Latch
Reset Write Enable Latch
Read Status Register
Write Status Register
Read Data from Array
Write Data to Array
Address
-
-
-
-
A15-A0
A15-A0
Data(SI)
-
-
-
D7-D0
-
D7-D0,...
Data (SO)
-
-
D7-D0,...
-
D7-D0,...
-
WREN 0000 X110
1. X = Don’t care bit. For consistency, it is best to use “0”.
2. Some address bits are don’t care. See Table 5.
3. If the bits clocked-in for an op-code are invalid, SO remains high impedance, and upon CS going High there is no
affect. A valid op-code with an invalid number of bits clocked-in for address or data will cause an attempt to modify
the array or Status Register to be ignored.
WRITE ENABLE (WREN)
When Vcc is initially applied, the device powers up with
both status register and entire array in a write-disabled
state. Upon completion of Write Disable (WRDI),
Write Status Register (WRSR), or Write Data to Array
(WRITE), the device resets the WEN bit in the Status
Register to 0. Prior to any data modification, a WREN
instruction is necessary to set WEN to 1. (See Figure 2
for timing).
WRITE DISABLE (WRDI)
The device can be completely protected from modifica-
tion by resetting WEN to 0 through the WRDI instruc-
tion. (See Figure 3 for timing).
READ STATUS REGISTER (RDSR)
The Read Status instruction tells the user the status of
Write Protect Enable, the Block Protection setting (see
Table 2), the Write Enable state, and the
RDY
status.
RDSR is the only instruction accepted when a write
cycle is underway. It is recommended that the status
of Write Enable and
RDY
be checked, especially prior
to an attempted modification of data. The 8 bits of the
Status Register can be repeatedly output on SO after
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