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CHAPTER 18 SERIAL INTERFACE CHANNEL 0 (
µ
PD78078Y Subseries)
“H”
SCL
SDA0 (SDA1)
(d) Acknowledge signal (ACK)
The acknowledge signal indicates that the transferred serial data has definitely been received. This
signal is used between the sending side and receiving side devices for confirmation of correct data
transfer. In principle, the receiving side device returns an acknowledge signal to the sending device
each time it receives 8-bit data. The only exception is when the receiving side is the master device and
the 8-bit data is the last transfer data; the master device outputs no acknowledge signal in this case.
The sending side that has tranferred 8-bit data waits for the acknowledge signal which will be sent from
the receiving side. If the sending side device receives the acknowledge signal, which means a successful
data transfer, it proceeds to the next processing. If this signal is not sent back from the slave device, this
means that the data sent has not been received by the slave device, and therefore the master device
outputs a stop condition signal to terminate subsequent transmissions.
Figure 18-18. Acknowledge Signal
(e) Stop condition
If the SDA0 (SDA1) pin level changes from low to high while the SCL pin is high, this transition is defined
as a stop condition signal.
The stop condition signal is output from the master to the slave device to terminate a serial transfer.
The stop condition signal is detected by hardware incorporated in the slave device.
Figure 18-19. Stop Condition
1 234567
A6 A5 A4 A3 A2 A1 A0 R/W
SCL
SDA0 (SDA1)
9
8
ACK