CDCUN1208LP datasheet(32/43 Pages) TI

32 / 43 page

STOP

START

I2C

ADDRESS

R/W

ACK

SDA

SCL

1 - 7

DATA

(HIGH

BYTE)

ACK

DATA

(LOW

BYTE)

ACK

I2C Address

R/W

7 Bits

1 Bit

Slave Address

7 Bits

Message

Addressing

and Control

Y/B

1 Bit

CDCUN1208LP

2C Address

Set by Pin 31

(ADDR)

Write: 0

Byte: 1

Block: 0

A3 A2 A1 A0

CDCUN1208LP

SCAS928 – MAY 2012

www.ti.com

Generic Message Frame

Figure 37 shows a typical format for I2C messages. The message frame is bracketed by the START and STOP

symbols (both generated by the master). If a START symbol has not been transmitted, then the bus is

considered ‘available’. If a START symbol has been transmitted and a STOP symbol has not been transmitted,

the bus is considered ‘busy’. The first 8 bits transmitted include the R/W bit and a 7-bit I2C address field. The

reception of each byte grouping that is transmitted must be acknowledged by the receiver. Next, the high byte of

the data pay load is transmitted (MSB first) followed by an acknowledgement by the receiver. Finally the low byte

is sent. After acknowledgement, the master sends a STOP symbol to end the message frame.

Figure 37. I2C Message Format

CDCUN1208LP Message Format

Figure 38 shows the format of addressing and flow control for I2C messages to/from the CDCUN1208LP. A

message includes two address fields. The I2C Address is used to support multiple devices on the bus (each

device must have a unique I2C address). The Register Address specifies which register of the device identified

by the I2C Address is to be written/read.

Figure 38. CDCUN1208LP I2C Message - Addressing

CDCUN1208LP Device Addressing (I2C Address)

Figure 38 outlines the construction of the I2C Address shown in Figure 37. The highest 6 bits are assigned to the

target device family (are unique to a specific target device family) and are ‘hard wired’. The lowest address bit

(A0) corresponds to address bit that can be set via pin 31 on the CDCUN1208LP (see Table 9). This allows up to

two CDCUN1208LPs to reside on the same I2C bus. The next 8 bits transmitted is called the Register Address.

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