NEC uPD78P078 - Manual (Page 453)

453
CHAPTER 19 SERIAL INTERFACE CHANNEL 1
(c) Bit slippage detection function through the busy signal
During an automatic transmit/receive operation, noise occur in the serial clock signal output by the
master device and bit slippage may occur in the slave device side serial clock. At this time, if the strobe
control option is not used, this bit slippage will have an effect on sending of the next byte. In such a
case, the busy control option can be used on the master device side and, by checking the busy signal
during sending, bit slippage can be detected.
Bit slippage detection through the busy signal is accomplished as follows.
The slave side outputs a busy signal after the serial clock rises on the 8th cycle of data sending or
receiving (at this time, if application of the wait state by the busy signal is not desired, the busy signal
is made inactive within 2 clock cycles).
The master device side samples the busy signal in sync with the fall of the serial clock’s front side. If
no bit slippage is occurring, the busy signal will be inactive in sampling for 8 clock cycles. If the busy
signal is found to be active in sampling, it is regarded as an occurrence of bit slippage error processing
is executed (bit 4 (ERR) of the automatic data transmit/receive control register (ADTC) is set at (1)).
The operation timing of the bit slippage detection function through the busy signal is shown in Figure
19-22.
Figure 19-22. Operation Timing of the Bit Slippage Detection Function through the Busy Signal
(BUSY0 = 1)
CSIIF1 : Interrupt request flag
CSIE1 : Bit 7 of serial operating mode register 1 (CSIM1)
ERR : Bit 4 of the automatic data transmit/receive control register (ADTC)
SCK1
D7 SO1
SI1
D6 D5 D4 D3 D2 D1 D0 D7 D6 D5 D4 D3 D2 D1 D0
D7 D6 D5 D4 D3 D2 D1 D0 D7 D6 D5 D4 D3 D2 D1 D0
BUSY
CSIIF1
CSIE1
ERR
D7
D7
No busy detection Error interrrupt request
generation
Error detection
(Slave Side)
SCK1
(Master Side)
Bit slippage due to noise