CHAPTER 13 SERIAL INTERFACE CHANNEL 0
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User’s Manual U11302EJ4V0UM
(f)
Busy signal (BUSY) and ready signal (READY)
The BUSY signal is used to report to the master device that the slave device is not ready for data
transmission/reception.
The READY signal is used to report to the master device that the slave device is ready for data
transmission/reception.
Figure 13-18. BUSY and READY Signals
In SBI, the slave device notifies the master device of the busy state by setting the SB0 (SB1) line to low
level.
BUSY signal output follows 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 the 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 SBI, after specifying reset of BUSY, the BUSY signal is output until the fall of the
next serial clock (SCK0). If WUP = 1 is set during this interval by mistake, it will be
impossible to reset BUSY. Therefore, after BUSY is released, make sure that the SB0
(SB1) pin is high level before setting WUP = 1.
(3) Register setting
The SBI mode is set by serial operating mode register 0 (CSIM0), the serial bus interface control register
(SBIC), and the interrupt timing specification register (SINT).
READY
ACK
SCK0
SB0 (SB1)
BUSY
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