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3874 Group User's Manual
APPLICATION
2.5 Serial I/O
2.5.15 Notes on serial I/O3
(1)
In all modes
s State of SOUT3 pin
q The SOUT3 output control bit of the serial I/O3 control register 2 can be used to select the state
of the SOUT3 pin when serial data is not transferred; either output active or high-impedance.
However, when selecting an external synchronous clock; the SOUT3 pin can become the high-
impedance state by setting the SOUT3 output control bit to “1” when SCLK3 input is at “H” after
transfer completion.
s Serial I/O initialization bit
q Set “0” to the serial I/O initialization bit of the serial I/O3 control register 1 when terminating a
serial transfer during transferring.
q When writing “1” to the serial I/O initialization bit, serial I/O3 is enabled, but each register is not
initialized. Set the value of each register by program.
s Handshake signal
q SBUSY3 input signal
Input an “H” level to the SBUSY3 input and an “L” level signal to the SBUSY3 input in the initial state.
When the external synchronous clock is selected, switch the input level to the SBUSY3 input and
the SBUSY3 input while the SCLK3 input is in “H” state.
q SRDY3 inputoutput signal
When selecting the internal synchronous clock, input an “L” level to the SRDY3 input and an “H”
level signal to the SRDY3 input in the initial state.
(2)
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/O3 register are being
shifted continually while the transfer clock is input to SCLK3. In this case, control the clock externally.
(3)
In automatic transfer serial I/O mode
s Set of automatic transfer interval
q When the SBUSY3 output is used, and the SBUSY3 output and the SSTB3 output function as signal for
each transfer data set by the SBUSY3 outputSSTB3 output function selection bit; the transfer interval
is necessary before the first data is transmitted/received, and after the last data is transmitted/
received. Accordingly, regardless of the contents of the SBUSY3 outputSSTB3 output function selection
bit, this transfer interval becomes 2 cycles longer than the value set for each 1-byte data.
q When using the SSTB3 output, regardless of the contents of the SBUSY3 outputSSTB3 output function
selection bit, this transfer interval becomes 2 cycles longer than the value set by the automatic
transfer interval select bit of the serial I/O3 control register 3 for each 1-byte data.
q When using the combined output of SBUSY3 and SSTB3 as the signal for each transfer data set, the
transfer interval after completion of transmission/reception of the last data becomes 2 cycles
longer than the value set by the automatic transfer interval select bit.
q Set the transfer interval of each 1-byte data transmission to 5 or more cycles of the internal
clock
φ after the rising edge of the last bit of a 1-byte data.
q When selecting an external clock, the automatic transfer interval cannot be set.