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38B5 Group User’s Manual
APPLICATION
2.3 Serial I/O
2.3.9 Notes on serial I/O1
(1) Clock
s Using internal clock
After setting the synchronous clock to an internal clock, clear the serial I/O interrupt request bit
before perform the normal serial I/O transfer or the serial I/O automatic transfer.
s Using external clock
After inputting “H” level to the external clock input pin, clear the serial I/O interrupt request bit
before performing the normal serial I/O transfer or the serial I/O automatic transfer.
(2) Using serial I/O1 interrupt
Clear bit 3 of the interrupt request register 1 to “0” by software.
(3)
State of SOUT1 pin
The SOUT1 pin control bit of the serial I/O1 control register 2 can be used to select the state of the
SOUT1 pin when serial data is not transferred; either output active or high-impedance. However, when
selecting an external synchronous clock; the SOUT1 pin can become the high-impedance state by
setting the SOUT1 pin control bit to “1” when the serial I/O1 clock input is at “H” after transfer completion.
(4)
Serial I/O initialization bit
q Set “0” to the serial I/O initialization bit of the serial I/O1 control register 1 when terminating a
serial transfer during transferring.
q When writing “1” to the serial I/O initialization bit, the serial I/O1 is enabled, but each register is
not initialized. Set the value of each register by program.
(5)
Handshake signal
s SBUSY1 input signal
Input an “H” level to the SBUSY1 input and an “L” level signal to the SBUSY1 input in the initial state.
When the external synchronous clock is selected, switch the input level to the SBUSY1 input and
the SBUSY1 input while the serial I/O1 clock input is in “H” state.
s SRDY1 inputoutput signal
When selecting the internal synchronous clock, input an “L” level to the SRDY1 input and an “H”
level signal to the SRDY1 input in the initial state.
(6)
8-bit serial I/O mode
s When selecting external synchronous clock
When an external synchronous clock is selected, the contents of the serial I/O1 register are being
shifted continually while the transfer clock is input to the serial I/O1 clock pin. In this case, control
the clock externally.
(7)
In automatic transfer serial I/O mode
s Set of automatic transfer interval
q When the SBUSY1 output is used, and the SBUSY1 output and the SSTB1 output function as signals
for each transfer data set by the SBUSY1 outputSSTB1 output function selection bit of serial I/O1
control register 2; the transfer interval is inserted before the first data is transmitted/received,
and after the last data is transmitted/received. Accordingly, regardless of the contents of the
SBUSY1 outputSSTB1 output function selection bit, this transfer interval for each 1-byte data becomes
2 cycles longer than the value set by the automatic transfer interval set bits of serial I/O1 control
register 3.