SDA

SCL

S

P

START condition

STO

P condition

LM48823, LM48823TLEVAL

SNAS464E – JUNE 2008 – REVISED OCTOBER 2010

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APPLICATION INFORMATION

I

2C COMPATIBLE INTERFACE

The LM48823 is controlled through an I2C compatible serial interface that consists of a serial data line (SDA) and

a serial clock (SCL). The clock line is uni-directional. The data line is bi-directional (open drain). The LM48823

and the master can communicate at clock rates up to 400kHz. Figure 18 shows the I2C interface timing diagram.

Data on the SDA line must be stable during the HIGH period of SCL. The LM48823 is a transmit/receive slave-

only device, reliant upon the master to generate the SCL signal. Each transmission sequence is framed by a

START condition and a STOP condition (Figure 19). Each data word, device address and data, transmitted over

the bus is 8 bits long and is always followed by an acknowledge pulse (Figure 20). The LM48823 device address

is 1110110.

I

2C BUS FORMAT

The I2C bus format is shown in Figure 20. The START signal, the transition of SDA from HIGH to LOW while

SCL is HIGH, is generated, alerting all devices on the bus that a device address is being written to the bus.

The 7-bit device address is written to the bus, most significant bit (MSB) first, followed by the R/W bit. R/W = 0

indicates the master is writing to the slave device, R/W = 1 indicates the master wants to read data from the

slave device. Set R/W = 0; the LM48823 is a WRITE-ONLY device and will not respond to the R/W = 1. The data

is latched in on the rising edge of the clock. Each address bit must be stable while SCL is HIGH. After the last

address bit is transmitted, the master device releases SDA, during which time, an acknowledge clock pulse is

generated by the slave device. If the LM48823 receives the correct address, the device pulls the SDA line low,

generating an acknowledge bit (ACK).

Once the master device registers the ACK bit, the 8-bit register data word is sent. Each data bit should be stable

while SCL is HIGH. After the 8-bit register data word is sent, the LM48823 sends another ACK bit. Following the

acknowledgement of the register data word, the master issues a STOP bit, allowing SDA to go high while SCL is

high.

Figure 18. I2C Timing Diagram

Figure 19. Start and Stop Diagram

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