NEC uPD78P078 User Manual
Page 339
CHAPTER 17 SERIAL INTERFACE CHANNEL 0 (
µ
PD78078 SUBSERIES)
339
(e) Acknowledge signal (ACK)
The acknowledge signal is used to check serial data reception between transmitter and receiver.
Figure 17-18. Acknowledge Signal
[When output in synchronization with 11th clock SCK0]
[When output in synchronization with 9th clock SCK0]
Remark
The brokens lines indicate the READY state.
The acknowledge signal is one-shot pulse to be generated at the falling edge of SCK0 after 8-bit data
transfer. It can be positioned anywhere and can be synchronized with any clock SCK0.
After 8-bit data transmission, the transmitter checks whether the receiver has returned the acknowledge
signal. If the acknowledge signal is not returned for the preset period of time after data transmission,
it can be judged that data reception has not been carried out correctly.
(f)
Busy signal (BUSY) and ready signal (READY)
The BUSY signal is intended to report to the master device that the slave device is preparing for data
transmission/reception.
The READY signal is intended to report to the master device that the slave device is ready for data
transmission/reception.
Figure 17-19. BUSY and READY Signals
In SBI, the slave device notifies the master device of the busy state by setting SB0 (SB1) line to the
low level.
The BUSY signal output follows the acknowledge signal output from the master or slave device. It is
set/reset at the falling edge of SCK0. When the BUSY signal is reset, the master device automatically
terminates the output of SCK0 serial clock.
When the BUSY signal is reset and the READY signal is set, the master device can start the next transfer.
Caution In the SBI mode, the BUSY signal continues to be output after BUSY clear instruction
generation to the falling edge of the next serial clock (SCK0). If WUP is set to 1 in this
period, BUSY will not be released. Therefore, before setting WUP to 1, clear BUSY and
then check that SB0 (SB1) pin has become high level.
SCK0
SB0 (SB1)
8
9
10
11
ACK
8
9
ACK
SCK0
SB0 (SB1)
READY
ACK
SCK0
SB0 (SB1)
BUSY
8
9