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(4)
Acknowledge (ACK) signal
The acknowledge (ACK) signal is used by the transmitting and receiving devices to confirm serial data
reception.
The receiving device returns one ACK signal for each 8 bits of data it receives. The transmitting device
normally receives an ACK signal after transmitting 8 bits of data. However, when the master device is the
receiving device, it does not output an ACK signal after receiving the final data to be transmitted.
transmitting device detects whether or not an ACK signal is returned after it transmits 8 bits of data. When an
ACK signal is returned, the reception is judged as normal and processing continues. If the slave device does
not return an ACK signal, the master device outputs either a stop condition or a restart condition and then stops
the current transmission. Failure to return an ACK signal may be caused by the following two factors.
(a) Reception was not performed normally.
(b) The final data was received.
When the receiving device sets the SDA line to low level during the ninth clock, the ACK signal becomes active
(normal receive response).
When bit 2 (ACKE) of the IIC control register (IICC0) is set to 1, automatic ACK signal generation is enabled.
Transmission of the eighth bit following the 7 address data bits causes bit 3 (TRC) of the IIC status register
(IICS0) to be set. When this TRC bit's value is "0", it indicates receive mode. Therefore, ACKE should be set to
"1".
When the slave device is receiving (when TRC = 0), if the slave devices does not need to receive any more
data after receiving several bytes, setting ACKE to "0" will prevent the master device from starting transmission
of the subsequent data.
Similarly, when the master device is receiving (when TRC = 0) and the subsequent data is not needed and
when either a restart condition or a stop condition should therefore be output, setting ACKE to "0" will prevent
the ACK signal from being returned. This prevents the MSB data from being output via the SDA line (i.e., stops
transmission) during transmission from the slave device.
SCL
SDA
236
CHAPTER 10 SERIAL INTERFACE FUNCTION
Figure 10-17. ACK Signal
1
2
3
4
A6
A5
A4
A3
5
6
7
8
9
A2
A1
A0
R/W ACK
The
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