Master Transmit Operation - Renesas H8S/2368 Series Hardware Manual

Legend
S: Start condition. The master device drives SDA from high to low while SCL is high.
SLA: Slave address
R/W: Indicates the direction of data transfer: from the slave device to the master device when
R/W is 1, or from the master device to the slave device when R/W is 0.
A: Acknowledge. The receiving device drives SDA to low.
DATA: Transferred data
P: Stop condition. The master device drives SDA from low to high while SCL is high.
15.4.2

Master Transmit Operation

2
In I C bus format 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 15.5 and 15.6. The transmission procedure and operations in master
transmit mode are described below.
1. Set the ICE bit in ICCRA to 1. Set the WAIT bit in ICMR and the CKS3 to CKS0 bits in
ICCR1 to 1. (Initial setting)
2. Read the BBSY flag in ICCRB to confirm that the bus is free. Set the MST and TRS bits in
ICCRA 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. After this, when TDRE is cleared to 0, 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, and clear TDRE and
TEND. 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.
5. The transmit data after the second byte is written to ICDRT every time TDRE is set, thus
clearing TDRE.
6. Write the number of bytes to be transmitted to ICDRT. Wait until TEND is set (the end of last
byte data transmission) while TDRE is 1, or wait for NACK (NACKF in ICSR = 1) from the
receive device while ACKE in ICIER is 1. Then, issue the stop condition to clear TEND or
NACKF.
7. When the STOP bit in ICSR is set to 1, the operation returns to the slave receive mode.
Rev. 2.00, 05/03, page 603 of 820