SH7721 datasheet(723/1524 Pages) RENESAS

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Section 20

2C Bus Interface (IIC)

Rev. 3.00 Jan. 18, 2008 Page 661 of 1458

REJ09B0033-0300

SDA

SCL

1-7

SLA

1-7

DATA

1-7

DATA

Figure 20.4

2C Bus Timing

[Legend]

Start condition. The master device drives SDA from high to low while SCL is high.

SLA:

Slave address

W: Indicates the direction of data transfer: from the slave device to the master device when

W is 1, or from the master device to the slave device when R/W is 0.

Acknowledge. The receive device drives SDA to low.

DATA: Transfer data

Stop condition. The master device drives SDA from low to high while SCL is high.

20.4.2

Master Transmit Operation

In master transmit mode, the master device outputs the transmit clock and transmit data, and the

slave device returns an acknowledge signal. For master transmit mode operation timing, refer to

figures 20.5 and 20.6. The transmission procedure and operations in master transmit mode are

described below.

1. Set the ICE bit in ICCR1 to 1. Set the MLS bit in ICMR and the CKS4 to CKS0 bits in ICCKS

to 1. (Initial setting)

2. Read the BBSY flag in ICCR2 to confirm that the bus is free. Set the MST and TRS bits in

ICCR1 to select master transmit mode. Then, write 1 to BBSY and 0 to SCP using MOV

instruction. (Start condition issued) This generates the start condition.

3. After confirming that TDRE in ICSR has been set, write the transmit data (the first byte data

show the slave address and R/

W) to ICDRT. At this time, TDRE is automatically cleared to 0,

and data is transferred from ICDRT to ICDRS. TDRE is set again.

4. When transmission of one byte data is completed while TDRE is 1, TEND in ICSR is set to 1

at the rise of the 9th transmit clock pulse. Read the ACKBR bit in ICIER, and confirm that the

slave device has been selected. Then, write second byte data to ICDRT. When ACKBR is 1,

the slave device has not been acknowledged, so issue the stop condition. To issue the stop

condition, write 0 to BBSY and SCP using MOV instruction. SCL is fixed low until the

transmit data is prepared or the stop condition is issued.

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