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RL78/G1A CHAPTER 13 SERIAL INTERFACE IICA
13.5.4 Acknowledge (ACK)
ACK is used to check the status of serial data at the transmission and reception sides.
The reception side returns ACK each time it has received 8-bit data.
The transmission side usually receives ACK after transmitting 8-bit data. When ACK is returned from the reception side,
it is assumed that reception has been correctly performed and processing is continued. Whether ACK has been detected
can be checked by using bit 2 (ACKD0) of the IICA status register 0 (IICS0).
When the master receives the last data item, it does not return ACK and instead generates a stop condition. If a slave
does not return ACK after receiving data, the master outputs a stop condition or restart condition and stops transmission.
If ACK is not returned, the possible causes are as follows.
Jul 04, 2013
<1> Reception was not performed normally.
<2> The final data item was received.
<3> The reception side specified by the address does not exist.
To generate ACK, the reception side makes the SDAA0 line low at the ninth clock (indicating normal reception).
Automatic generation of ACK is enabled by setting bit 2 (ACKE0) of IICA control register 00 (IICCTL00) to 1. Bit 3
(TRC0) of the IICS0 register is set by the data of the eighth bit that follows 7-bit address information. Usually, set the
ACKE0 bit to 1 for reception (TRC0 = 0).
If a slave can receive no more data during reception (TRC0 = 0) or does not require the next data item, then the slave
must inform the master, by clearing the ACKE0 bit to 0, that it will not receive any more data.
When the master does not require the next data item during reception (TRC0 = 0), it must clear the ACKE0 bit to 0 so
that ACK is not generated. In this way, the master informs a slave at the transmission side that it does not require any
more data (transmission will be stopped).
Figure 13-18. ACK
SCLA0
SDAA0
123456789
A6 A5 A4 A3 A2 A1 A0 R/W
ACK
When the local address is received, ACK is automatically generated, regardless of the value of the ACKE0 bit. When
an address other than that of the local address is received, ACK is not generated (NACK).
When an extension code is received, ACK is generated if the ACKE0 bit is set to 1 in advance.
How ACK is generated when data is received differs as follows depending on the setting of the wait timing.
• When 8-clock wait state is selected (bit 3 (WTIM0) of IICCTL00 register = 0):
By setting the ACKE0 bit to 1 before releasing the wait state, ACK is generated at the falling edge of the eighth clock
of the SCLA0 pin.
• When 9-clock wait state is selected (bit 3 (WTIM0) of IICCTL00 register = 1):
ACK is generated by setting the ACKE0 bit to 1 in advance.
R01UH0305EJ0200 Rev.2.00 592