R8C/1A Group, R8C/1B Group
16. Clock Synchronous Serial Interface
Rev.1.30
Dec 08, 2006
Page 212 of 315
REJ09B0252-0130
16.3.3.2
Master Transmit Operation
In master transmit mode, the master device outputs the transmit clock and data, and the slave device returns an
acknowledge signal.
Figures 16.33 and 16.34 show the Operating Timing in Master Transmit Mode (I
2
C bus Interface Mode).
The transmit procedure and operation in master transmit mode are as follows.
(1) Set the STOP bit in the ICSR register to 0 to reset it. Then set the ICE bit in the ICCR1 register to 1
(transfer operation enabled). Then set bits WAIT and MLS in the ICMR register and set bits CKS0 to
CKS3 in the ICCR1 register (initial setting).
(2) Read the BBSY bit in the ICCR2 register to confirm that the bus is free. Set bits TRS and MST in the
ICCR1 register to master transmit mode. The start condition is generated by writing 1 to the BBSY bit
and 0 to the SCP bit by the MOV instruction.
(3) After confirming that the TDRE bit in the ICSR register is set to 1 (data is transferred from registers
ICDRT to ICDRS), write transmit data to the ICDRT register (data in which a slave address and R/W
are indicated in the 1st byte). At this time, the TDRE bit is automatically set to 0, data is transferred
from registers ICDRT to ICDRS, and the TDRE bit is set to 1 again.
(4) When transmission of 1 byte of data is completed while the TDRE bit is set to 1, the TEND bit in the
ICSR register is set to 1 at the rise of the 9th transmit clock pulse. Read the ACKBR bit in the ICIER
register, and confirm that the slave is selected. Write the 2nd byte of data to the ICDRT register. Since
the slave device is not acknowledged when the ACKBR bit is set to 1, generate the stop condition. The
stop condition is generated by the writing 0 to the BBSY bit and 0 to the SCP bit by the MOV
instruction. The SCL signal is held “L” until data is available and the stop condition is generated.
(5) Write the transmit data after the 2nd byte to the ICDRT register every time the TDRE bit is set to 1.
(6) When writing the number of bytes to be transmitted to the ICDRT register, wait until the TEND bit is
set to 1 while the TDRE bit is set to 1. Or wait for NACK (the NACKF bit in the ICSR register is set to
1) from the receive device while the ACKE bit in the ICIER register is set to 1 (when the receive
acknowledge bit is set to 1, transfer is halted). Then generate the stop condition before setting bits
TEND and NACKF to 0.
(7) When the STOP bit in the ICSR register is set to 1, return to slave receive mode.
