CHAPTER 15 SERIAL INTERFACE IICA
Page 452 of 920
15.5.4Acknowledge (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 (ACKDn) of the IICA status register n (IICSn).
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.
<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 SDAAn line low at the ninth clock (indicating normal reception).
Automatic generation of ACK is enabled by setting bit 2 (ACKEn) of IICA control register n0 (IICCTLn0) to 1. Bit
3 (TRCn) of the IICSn register is set by the data of the eighth bit that follows 7-bit address information. Usually,
set the ACKEn bit to 1 for reception (TRCn = 0).
If a slave can receive no more data during reception (TRCn = 0) or does not require the next data item, then the
slave must inform the master, by clearing the ACKEn bit to 0, that it will not receive any more data.
When the master does not require the next data item during reception (TRCn = 0), it must clear the ACKEn 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 15 - 23 ACK
When the local address is received, ACK is automatically generated, regardless of the value of the ACKEn 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 ACKEn 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 (WTIMn) of IICCTLn0 register = 0):
By setting the ACKEn bit to 1 before releasing the wait state, ACK is generated at the falling edge of the eighth
clock of the SCLAn pin.
• When 9-clock wait state is selected (bit 3 (WTIMn) of IICCTLn0 register = 1):
ACK is generated by setting the ACKEn bit to 1 in advance.
Remark
n = 0, 1
SCLAn
SDAAn
1
2
3
4
5
6
7
8
9
A6
A5
A4
A3
A2
A1
A0
R/W ACK
Summary of Contents for RL78/G1H
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