CAT24C208
www.onsemi.com
5
I
2
C Bus Protocol
The following defines the features of the I
2
C bus protocol:
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 either
SDA when the respective SCL is HIGH. The CAT24C208
monitors 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.
Acknowledge
After a successful data transfer, each receiving device is
required to generate an acknowledge. The acknowledging
device pulls down the respective SDA line during the ninth
clock cycle, signaling that it received the 8 bits of data.
The CAT24C208 responds with an acknowledge after
receiving a START condition and its slave address. If the
device has been selected along with a write operation, it
responds with an acknowledge after receiving each 8−bit
byte.
When the CAT24C208 is in a READ mode it transmits 8
bits of data, releases the respective SDA line, and monitors
the line for an acknowledge. Once it receives this
acknowledge, the CAT24C208 will continue to transmit
data. If no acknowledge is sent by the Master, the device
terminates data transmission and waits for a STOP
condition.
After an unsuccessful data transfer an acknowledge will
not be issued (NACK) by the slave (CAT24C208), and the
master should abort the sequence. If continued the device
will read from or write to the wrong address in the two
instruction format with the segment pointers.
Figure 5. Acknowledge Timing
START
SCL FROM
MASTER
BUS RELEASE DELAY (TRANSMITTER)
ACK DELAY
ACK SETUP
BUS RELEASE DELAY
DATA OUTPUT
FROM TRANSMITTER
DATA OUTPUT
FROM RECEIVER
(RECEIVER)
189
Device Addressing
DDC Interface
Both the DDC and DSP interfaces to the device are based
on the I
2
C bus serial interface. All memory space operations
are done at the A0/A1 DDC address pair. As such, all write
operations to the memory space are done at DDC address
A0h and all read operations of the memory space are done
at DDC address A1h.
Figure 6 shows the bit sequence of a random read from
anywhere within the memory space. The word offset
determines which of the 256 bytes within segment 00h is
being read. Here the segment 00h can be at the lower or
upper bank depending on the configuration register.
Sequential reads can be done in much the same manner by
reading successive bytes after each acknowledge without
generating a stop condition. See Figure 7. The device
automatically increments the word offset value (8−bit value)
and with wraparound in the same segment 00h to read
maximum of 256 bytes.
