without notice. 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 before placing orders for products.
Integrated Silicon Solution, Inc. — 1-800-379-4774
ADVANCED INFORMATION Rev. 00B
05/05/04
1
IS24C32A/B
IS24C64A/B
FUNCTIONAL BLOCK DIAGRAM
ISSI
HIGH VOLTAGE
GENERATOR,
TIMING & CONTROL
®
Vcc
8
SDA
SCL
WP
5
7
X
DECODER
6
CONTROL
LOGIC
SLAVE ADDRESS
REGISTER &
COMPARATOR
EEPROM
ARRAY
A0
A1
A2
1
2
3
WORD ADDRESS
COUNTER
Y
DECODER
GND
4
ACK
Clock
DI/O
>
nMOS
DATA
REGISTER
PIN DESCRIPTIONS
A0-A2
SDA
SCL
WP
Vcc
GND
Address Inputs
Serial Address/Data I/O
Serial Clock Input
Write Protect Input
Power Supply
Ground
PIN CONFIGURATION
8-Pin DIP, SOIC, and TSSOP
A0
A1
A2
GND
1
2
3
4
8
7
6
5
VCC
WP
SCL
SDA
SCL
This input clock pin is used to synchronize the data
transfer to and from the device.
WP
WP is the Write Protect pin. The input level determines if all,
partial, or none of the array is protected from modifications.
Write Protection
Array Addresses Protected
WP
GND or floating
Vcc
IS24C32A/64A
None
Entire Array
IS24C32B
None
C00h
-FFFh
IS24C64B
None
1800h
-1FFFh
SDA
The SDA is a Bi-directional pin used to transfer addresses
and data into and out of the device. The SDA pin is an open
drain output and can be wire-Ored with other open drain
or open collector outputs. The SDA bus
requires
a pullup
resistor to Vcc.
A0, A1, A2
The A0, A1 and A2 are the device address inputs that are
hardwired or left not connected for hardware compatibility
with the 24C16. When pins are hardwired, as many as eight
32K/64K devices may be addressed on a single bus
system. When the pins are not hardwired, the default values
of A0, A1, and A2 are zero.
2
Integrated Silicon Solution, Inc. — 1-800-379-4774
ADVANCED INFORMATION Rev. 00B
05/05/04
IS24C32A/B
IS24C64A/B
ISSI
Stop Condition
®
DEVICE OPERATION
IS24CXX features serial communication and supports a bi-
directional 2-wire bus transmission protocol.
2-WIRE BUS
The two-wire bus is defined as a Serial Data line (SDA), and
a Serial Clock line (SCL). The protocol defines any device
that sends data onto the SDA bus as a transmitter, and the
receiving devices as a receiver. The bus is controlled by a
Master device that generates the SCL, controls the bus
access, and generates the Stop and Start conditions. The
IS24CXX is the Slave device on the bus.
The Stop condition is defined as a Low to High transition of
SDA when SCL is High. All operations must end with a Stop
condition.
Acknowledge (ACK)
After a successful data transfer, each receiving device is
required to generate an ACK. The Acknowledging device
pulls down the SDA line.
Reset
The
IS24CXX
contains a reset function in case the 2-
wire bus transmission is accidentally interrupted (eg. a
power loss), or needs to be terminated mid-stream. The
reset is caused when the Master device creates a Start
condition. To do this, it may be necessary for the Master
device to monitor the SDA line, which may cycle the
SCL up to nine times. (For each clock signal transition to
High, the Master checks for a High level on SDA.)
The Bus Protocol:
– Data transfer may be initiated only when the bus is not
busy
– During a data transfer, the data line must remain stable
whenever the clock line is high. Any changes in the data
line while the clock line is high will be interpreted as a
Start or Stop condition.
The state of the data line represents valid data after a Start
condition. The data line must be stable for the duration of the
High period of the clock signal. The data on the SDA line
may be changed during the Low period of the clock signal.
There is one clock pulse per bit of data. Each data transfer
is initiated with a Start condition and terminated with a Stop
condition.
Standby Mode
Power consumption is reduced in standby mode. The
IS24CXX will enter standby mode: a) At Power-up, and
remain in it until SCL or SDA toggles; b) Following the Stop
signal if a no write operation is initiated; or c) Following any
internal write operation.
Start Condition
The Start condition precedes all commands to the device
and is defined as a High to Low transition of SDA when SCL
is High. The EEPROM monitors the SDA and SCL lines and
will not respond until the Start condition is met.
Integrated Silicon Solution, Inc. — 1-800-379-4774
ADVANCED INFORMATION Rev. 00B
05/05/04
3
IS24C32A/B
IS24C64A/B
DEVICE ADDRESSING
The Master begins a transmission by sending a Start
condition. The Master then sends the address of the
particular Slave devices it is requesting. The Slave
(Fig. 5) address is 8 bits.
The four most significant bits of the address are fixed as
1010 for the IS24CXX.
The next three bits of the Slave address are A0, A1, and A2,
and are used in comparison with the hard-wired input values
on the A0, A1, and A2 pins. Up to eight IS24CXX units may
share the 2-wire bus.
The last bit of the Slave address specifies whether a Read
or Write operation is to be performed. When this bit is set
to 1, a Read operation is selected, and when set to 0, a Write
operation is selected.
After the Master transmits the Start condition and Slave
address byte (Fig. 5), the appropriate 2-wire Slave
(eg.IS24C64A) will respond with ACK on the SDA line. The
Slave will pull down the SDA on the ninth clock cycle,
signaling that it received the eight bits of data. The selected
EEPROM then prepares for a Read or Write operation by
monitoring the bus.
ISSI
WRITE OPERATION
Byte Write
®
In the Byte Write mode, the Master device sends the Start
condition and the Slave address information (with the R/W
set to Zero) to the Slave device. After the Slave generates
an ACK, the Master sends the two byte address that is to
be written into the address pointer of the IS24CXX. After
receiving another ACK from the Slave, the Master device
transmits the data byte to be written into the address
memory location. The IS24CXX acknowledges once more
and the Master generates the Stop condition, at which time
the device begins its internal programming cycle. While
this internal cycle is in progress, the device will not respond
to any request from the Master device.
Page Write
The IS24CXX is capable of 32-byte Page-Write operation. A
Page-Write is initiated in the same manner as a Byte Write,
but instead of terminating the internal Write cycle after the
first data word is transferred, the Master device can transmit
up to 31 more bytes. After the receipt of each data word, the
EEPROM responds immediately with an ACK on SDA line,
and the five lower order data word address bits are internally
incremented by one, while the higher order bits of the data
word address remain constant. If a byte address is
incremented from the last byte of a page, it returns to the
first byte of that page. If the Master device should transmit
more than 32 bytes prior to issuing the Stop condition, the
address counter will “roll over,” and the previously written data
will be overwritten. Once all 32 bytes are received and the
Stop condition has been sent by the Master, the internal
programming cycle begins. At this point, all received data is
written to the IS24CXX in a single Write cycle. All inputs are
disabled until completion of the internal Write cycle.
Acknowledge (ACK) Polling
The disabling of the inputs can be used to take advantage
of the typical Write cycle time. Once the Stop condition is
issued to indicate the end of the host's Write operation, the
IS24CXX initiates the internal Write cycle. ACK polling can
be initiated immediately. This involves issuing the Start
condition followed by the Slave address for a Write operation.
If the EEPROM is still busy with the Write operation, no ACK
will be returned. If the IS24CXX has completed the Write
operation, an ACK will be returned and the host can then
proceed with the next Read or Write operation.
4
Integrated Silicon Solution, Inc. — 1-800-379-4774
ADVANCED INFORMATION Rev. 00B
05/05/04
IS24C32A/B
IS24C64A/B
READ OPERATION
Read operations are initiated in the same manner as Write
operations, except that the (R/W) bit of the Slave address
is set to “1”. There are three Read operation options: current
address read, random address read and sequential read.
ISSI
Random Address Read
®
Current Address Read
The IS24CXX contains an internal address counter which
maintains the address of the last byte accessed, incremented
by one. For example, if the previous operation is either a
Read or Write operation addressed to the address location
n, the internal address counter would increment to address
location n+1. When the EEPROM receives the Slave
Addressing Byte with a Read operation (R/W bit set to “1”),
it will respond an ACK and transmit the 8-bit data byte stored
at address location n+1. The Master should not acknowledge
the transfer but should generate a Stop condition so the
IS24CXX discontinues transmission. If 'n' is the last byte
of the memory, then the data from location '0' will be
transmitted. (Refer to Figure 8. Current Address Read
Diagram.)
Selective Read operations allow the Master device to
select at random any memory location for a Read
operation. The Master device first performs a 'dummy'
Write operation by sending the Start condition, Slave
address and byte address of the location it wishes to read.
After the IS24CXX acknowledges the byte address, the
Master device resends the Start condition and the Slave
address, this time with the R/W bit set to one. The
EEPROM then responds with its ACK and sends the data
requested. The Master device does not send an ACK but
will generate a Stop condition. (Refer to Figure 9. Random
Address Read Diagram.)
Sequential Read
Sequential Reads can be initiated as either a Current
Address Read or Random Address Read. After the IS24CXX
sends initial byte sequence, the Master device now responds
with an ACK indicating it requires additional data from the
IS24CXX. The EEPROM continues to output data for each
ACK received. The Master device terminates the sequential
Read operation by pulling SDA High (no ACK) indicating the
last data word to be read, followed by a Stop condition.
The data output is sequential, with the data from address n
followed by the data from address n+1, n+2 ... etc. The
address counter increments by one automatically, allowing
the entire memory contents to be serially read during
sequential Read operation. When the memory address
boundary of 8191 for IS24C64A/B or 4095 for IS24C32A/B
(depending on the device) is reached, the address counter
“rolls over” to address 0, and the device continues to output
data. (Refer to Figure 10. Sequential Read Diagram).
Integrated Silicon Solution, Inc. — 1-800-379-4774
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