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(4) Acknowledge signal (ACK)
The acknowledge signal is a signal for checking serial data reception in the transmit and receive sides.
The receive side sends back the acknowledge signal each time it receives an 8-bit data. The transmit side
receives the acknowledge signal after transmitting the 8-bit data. However, in the case the master is the receive
side, no acknowledge signal is output if the master receives the final data. The transmit side detects whether
the receive side has sent the acknowledge signal back to the transmit side after transmitting 8 bits. If the
acknowledge signal is sent back, the transmit side continues processing considering that reception has been
performed correctly. If the slave does not send back the acknowledge signal, the reception has not been
performed correctly. Therefore, the master outputs a stop condition or restart condition and aborts the
transmission. If the acknowledge signal is not sent back, the following two factors can be considered.
<1> The receptions has not been performed correctly.
<2> The final data has been received.
When the receive side sets the SDA line to low level at the ninth clock, the acknowledge signal (ACK) becomes
active (normal reception response).
When ACKE of the IICC register = 1, the acknowledge signal automatic generation enable status is set.
The TRC bit of the IICS register is set according to the data of the eighth bit following the 7-bit address
information. However, when the value of the TRC bit is 0, set ACKE = 1, because it is receive status.
In the slave receive operation (TRC = 0), if the slave side has received two or more bytes and needs the next
data, set ACKE = 0 so that the master side is disabled to start the next transfer.
Similarly, in the master receive operation (TRC = 0), if the master side receives two or more bytes and needs
the next data, set ACKE = 0 to output the restart condition or the stop condition so that the ACK signal does
not generate. This prevents the MSB data from being output to the SDA line in the slave transmit operation
(transmission stops).
SCL
SDA
When receiving the local address, the acknowledge signal is automatically output in synchronization with the
fall of the eighth clock of SCL regardless of the value of the ACKE. The acknowledge signal is not output
when receiving an address other than the local address.
The output methods of the acknowledge signal are as follows according to the setting of the wait timing.
• When selecting 8-clock wait : acknowledge signal is output by setting ACKE = 1 before releasing wait.
• When selecting 9-clock wait : acknowledge signal is automatically output in synchronization with the
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CHAPTER 8 SERIAL INTERFACE FUNCTION
Figure 8-18. Acknowledge Signal
1
2
3
4
A6
A5
A4
A3
fall of the eighth clock of SCL by setting ACKE = 1 beforehand.
User's Manual U11969EJ3V0UM00
5
6
7
8
A2
A1
A0
R/W
9
ACK
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