Preliminary Information
CAT1021, CAT1022, CAT1023
SDA when SCL is HIGH. The CAT1021/22/23 monitor
the SDA and SCL lines and will not respond until this
condition is met.
EMBEDDED EEPROM OPERATION
The CAT1021/22/23 feature a 2kbit embedded serial
EEPROM that supports the I2C Bus data transmission
protocol.ThisInter-IntegratedCircuitBusprotocoldefines
any device that sends data to the bus to be a transmitter
and any device receiving data to be a receiver. The
transfer is controlled by the Master device which
generates the serial clock and all START and STOP
conditions for bus access. Both the Master device and
Slavedevicecanoperateaseithertransmitterorreceiver,
but the Master device controls which mode is activated.
STOP Condition
A LOW to HIGH transition of SDA when SCL is HIGH
determinestheSTOPcondition.Alloperationsmustend
with a STOP condition.
DEVICE ADDRESSING
The Master begins a transmission by sending a START
condition.TheMastersendstheaddressoftheparticular
slave device it is requesting. The four most significant
bitsofthe8-bitslaveaddressareprogrammableinmetal
and the default is 1010.
I2C Bus Protocol
The features of the I2C bus protocol are defined as
follows:
(1) Data transfer may be initiated only when the bus is
not busy.
The last bit of the slave address specifies whether a
ReadorWriteoperationistobeperformed.Whenthisbit
is set to 1, a Read operation is selected, and when set
to 0, a Write operation is selected.
(2) During a data transfer, the data line must remain
stable whenever the clock line is high. Any changes in
thedatalinewhiletheclocklineishighwillbeinterpreted
as a START or STOP condition.
After the Master sends a START condition and the slave
address byte, the CAT1021/22/23 monitors the bus and
responds with an acknowledge (on the SDA line) when
its address matches the transmitted slave address. The
CAT1021/22/23 then perform a Read or Write operation
depending on the R/W bit.
START Condition
The START Condition precedes all commands to the
device, and is defined as a HIGH to LOW transition of
Figure 3. Bus Timing
t
t
t
F
HIGH
R
t
t
LOW
LOW
SCL
t
t
HD:DAT
SU:STA
t
t
t
t
HD:STA
SU:DAT
SU:STO
SDA IN
BUF
t
t
DH
AA
SDA OUT
Figure 4. Write Cycle Timing
SCL
SDA
8TH BIT
BYTE n
ACK
t
WR
STOP
CONDITION
START
CONDITION
ADDRESS
Doc No. 3009, Rev. E
9
CATALYST [ CATALYST SEMICONDUCTOR ]
