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CHAPTER 18 SERIAL INTERFACE CHANNEL 1
(b) Basic transmission mode
In this mode, the specified number of 8-bit unit data are transmitted.
Serial transfer is started when any data is written to the serial I/O shift register 1 (SIO1) while bit 7 (CSIE1)
of the serial operating mode register 1 (CSIM1) is set to 1.
The interrupt request flag (CSIIF1) is set upon completion of transmission of the last byte. However, judge
the completion of the automatic transmission/reception not with CSIIF1 but bit 3 (TRF) of the automatic
data transmit/receive control register (ADTC).
If receive operation, busy control and strobe control are not executed, the P20/SI1, P23/STB and P24/
BUSY pins can be used as normal input/ports.
Figure 18-11 shows the basic transmission mode operation timings, and Figure 18-12 shows the operation
flowchart. Figure 18-13 shows the operation of the buffer RAM when 6 bytes of data are transmitted or
received.
Figure 18-11. Basic Transmission Mode Operation Timings
Cautions 1. Because, in the basic transmission mode, the automatic transmit/receive function
reads data from the buffer RAM after 1-byte transmission, an interval is inserted till
the next transmission. As the buffer RAM read is performed at the same time as CPU
processing, the maximum interval is dependent upon CPU processing and the value
of the automatic data transmit/receive interval specify register (ADTI) (see (5)
"Automatic data transmit/receive interval").
2. When TRF is cleared, the SO1 pin becomes low level.
Remark CSIIF1 : Interrupt request flag
TRF : Bit 3 of automatic data transmit/receive control register (ADTC)
SCK1
SO1 D7 D6 D5 D4 D3 D2 D1 D0 D7 D6 D5 D4 D3 D2 D1 D0
CSIIF1
TRF
Interval