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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.
When the final byte has been sent, an interrupt request flag (CSIIF1) is set. However, judge the termination
of automatic transmit and receive, not by CSIIF1 but by 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/TxD1 and
P24/BUSY/RxD1 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 internal 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 internal 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