X4643 datasheet(8/21 Pages) RENESAS

8 / 21 page

X4643, X4645

FN8123 Rev 0.00

Page 8 of 21

March 29, 2005

Serial Start Condition

All commands are preceded by the start condition, which

is a HIGH to LOW transition of SDA when SCL is HIGH.

The device continuously monitors the SDA and SCL

lines for the start condition and will not respond to any

command until this condition has been met. See Figure

Serial Stop Condition

All communications must be terminated by a stop condi-

tion, which is a LOW to HIGH transition of SDA when SCL

is HIGH. The stop condition is also used to place the

device into the Standby power mode after a read

sequence. A stop condition can only be issued after the

transmitting device has released the bus. See Figure 6.

Figure 6. Valid Start and Stop Conditions

Serial Acknowledge

Acknowledge is a software convention used to indicate

successful data transfer. The transmitting device, either

master or slave, will release the bus after transmitting

eight bits. During the ninth clock cycle, the receiver will

pull the SDA line LOW to acknowledge that it received

the eight bits of data. Refer to Figure 7.

The device will respond with an acknowledge after rec-

ognition of a start condition and if the correct Device

Identifier and Select bits are contained in the Slave

Address Byte. If a write operation is selected, the device

will respond with an acknowledge after the receipt of

each subsequent eight bit word. The device will

acknowledge all incoming data and address bytes,

except for the Slave Address Byte when the Device

Identifier and/or Select bits are incorrect.

In the read mode, the device will transmit eight bits of

data, release the SDA line, then monitor the line for an

acknowledge. If an acknowledge is detected and no stop

condition is generated by the master, the device will con-

tinue to transmit data. The device will terminate further

data transmissions if an acknowledge is not detected.

The master must then issue a stop condition to return

the device to Standby mode and place the device into a

known state.

Figure 7. Acknowledge Response From Receiver

SCL

SDA

Start

Stop

Data Output

from

Data Output

from Receiver

Start

Acknowledge

SCL from

Master

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