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CHAPTER 14
SERIAL INTERFACE SIO1
User’s Manual U12790EJ2V0UD
When using the busy control option, select the internal clock as the serial clock. Control by the busy signal
cannot be implemented with the external clock.
Figure 14-19 shows the operation timing when the busy control option is used.
Caution
Busy control cannot be used simultaneously with the interval time control function of
the automatic data transmit/receive interval specification register (ADTI). If used, busy
control is invalid.
Figure 14-19. Operation Timing When Busy Control Option Is Used (When BUSY0 = 0)
Caution
If TRF is cleared, the SO1 pin goes low.
Remark
CSIIF1: Interrupt request flag
TRF:
Bit 3 of the automatic data transmit/receive control register (ADTC)
When the busy signal becomes inactive, waiting is released. If the sampled busy signal is inactive,
transmission/reception of the next 8-bit data is started at the falling edge of the next clock.
Because the busy signal is asynchronous to the serial clocks, it takes up to 1 clock until the busy signal,
even if made inactive by the slave, is sampled. It takes 0.5 clocks until data transfer is started after the
busy signal was sampled.
To accurately release waiting, the slave must keep the busy signal inactive for at least the duration of
1.5 clocks.
Figure 14-20 shows the timing of the busy signal and wait release. This figure shows an example where
the busy signal is active as soon as transmission/reception has been started.
SCK1
D7
SO1
SI1
CSIIF1
D6 D5 D4 D3 D2 D1 D0
D7 D6 D5 D4 D3 D2 D1 D0
BUSY
TRF
Busy input released
Busy input valid
Wait