NEC uPD78056Y - Manual (Page 314)

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CHAPTER 16 SERIAL INTERFACE CHANNEL 0 (
µ
PD78054 Subseries)
(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 16-19. 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 SBI outputs the BUSY signal after BUSY has been cleared until the next falling edge of
the serial clock. If WUP is set to 1 by mistake during this time, BUSY will not be cleared.
Therefore, when setting WUP to 1, do so after clearing BUSY and then making sure that
the SB0 (SB1) pin has gone high.
READY ACK
SCK0
SB0 (SB1) BUSY
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