CAT1161, CAT1162
FUNCTIONAL DESCRIPTION
The CAT1161/2 supports the I
2
C Bus data transmis–
sion protocol. This Inter-Integrated Circuit Bus proto–
col defines 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 Slave device can operate as either
transmitter or receiver, but the Master device controls
which mode is activated.
I C BUS PROTOCOL
The features of the I
2
C bus protocol are defined as
follows:
(1) Data transfer may be initiated only when the bus
is not busy.
(2) 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.
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 CAT1161/2 monitors
Figure 5. Acknowledge Timing
2
the SDA and SCL lines and will not respond until this
condition is met.
STOP Condition
A LOW to HIGH transition of SDA when SCL is HIGH
determines the STOP condition. All operations must
end with a STOP condition.
Device Addressing
The Master begins a transmission by sending a
START condition. The Master sends the address of
the particular slave device it is requesting. The four
most significant bits of the 8-bit slave address are
fixed as 1010.
The next three bits (Figure 6) define memory
addressing. For the CAT1161/2 the three bits define
higher order bits.
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 sends a START condition and the
slave address byte, the CAT1161/2 monitors the bus
and responds with an acknowledge (on the SDA line)
when its address matches the transmitted slave
address. The CAT1161/2 then performs a Read or
¯¯
Write operation depending on the R/W bit.
SCL FROM
MASTER
1
8
9
DATA OUTPUT
FROM TRANSMITTER
DATA OUTPUT
FROM RECEIVER
START
ACKNOWLEDGE
Figure 6. Slave Address Bits
CAT1161/2
1
0
1
0
a10
a9
a8
¯¯
R/W
**a8, a9 and a10 correspond to the address of the memory array address word.
© Catalyst Semiconductor, Inc.
Characteristics subject to change without notice
7
Doc. No. MD-3002 Rev. G
CATALYST [ CATALYST SEMICONDUCTOR ]
