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CHAPTER 14
SERIAL INTERFACE SIO1
User’s Manual U12790EJ2V0UD
(3) Communication operation
(a) Basic transmit/receive mode
This transmit/receive mode is the same as the 3-wire serial I/O mode in which the specified number of
data are transmitted/received in 8-bit units.
Serial transfer is started when any data is written to serial I/O shift register 1 (SIO1) while bit 7 (CSIE1)
of serial operating mode register 1 (CSIM1) is set to 1.
Upon completion of transmission of the last byte, the interrupt request flag (CSIIF1) is set. The termination
of automatic transmission/reception should be checked by using bit 3 (TRF) of the automatic data transmit/
receive control register (ADTC), not by CSIIF1 because the CSIIF1 interrupt request flag is cleared if an
interrupt is acknowledged.
If busy control and strobe control are not executed, the P23/STB and P24/BUSY pins can be used as
normal I/O ports.
Figure 14-8 shows the basic transmit/receive mode operation timing, and Figure 14-9 shows the operation
flowchart.
Figure 14-10 shows the buffer RAM operation in 6-byte transmission.
Figure 14-8. Basic Transmit/Receive Mode Operation Timing
Cautions 1. Because, in the basic transmit/receive mode, the automatic transmit/receive function
writes/reads data to/from the buffer RAM after 1-byte transmission/reception, an
interval is inserted until the next transmission/reception. As the buffer RAM write/
read is performed at the same time as CPU processing, the maximum interval is
dependent upon the CPU processing and the value of the automatic data transmit/
receive interval specification register (ADTI) (refer to (6) Automatic data transmit/
receive interval).
2. When TRF is cleared, the SO1 pin becomes low level.
Remark
CSIIF: Interrupt request flag
TRF:
Bit 3 of the automatic data transmit/receive control register (ADTC)
SCK1
SO1
D7 D6 D5 D4 D3 D2 D1 D0
CSIIF1
TRF
SI1
D7 D6 D5 D4 D3 D2 D1 D0
Interval