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CHAPTER 17 SERIAL INTERFACE CHANNEL 0 (
µ
PD78054Y Subseries)
(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 17-18. 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 17-19. Stop Condition
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A6 A5 A4 A3 A2 A1 A0 R/W
SCL
SDA0 (SDA1)
9
8
ACK
H
SCL
SDA0(SDA1)