Acknowledge (Ack) - NEC 78K0 Series User Manual

17.5.4 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 IIC 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.
<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 SDA0 line low at the ninth clock (indicating normal reception).
Automatic generation of ACK is enabled by setting bit 2 (ACKE0) of IIC control register 0 (IICC0) 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 ACKE0 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 ACKE0 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 ACKE0 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).
SCL0
SDA0
When the local address is received, ACK is automatically generated, regardless of the value of ACKE0. 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 ACKE0 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 IICC0 register = 0):
By setting ACKE0 to 1 before releasing the wait state, ACK is generated at the falling edge of the eighth clock of
the SCL0 pin.
• When 9-clock wait state is selected (bit 3 (WTIM0) of IICC0 register = 1):
ACK is generated by setting ACKE0 to 1 in advance.
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CHAPTER 17 SERIAL INTERFACE IIC0
Figure 17-16. ACK
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A6 A5 A4 A3 A2
Preliminary User's Manual U17260EJ3V1UD
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A1 A0 R/W ACK