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Serial I/O2
2.6 Serial I/O2
2.6.1 Overview
Serial I/O2 performs 8-bit data serial communication, synchronized with the clocks. In the automatic
transfer serial I/O mode, serial communication of up to 256 bytes can be continuously performed without
use of the CPU. The following is the Serial I/O2 overview.
(1) Transfer format
Transfer format is 8-bit data.
(2) Transfer rate
When selecting an internal clock as the transfer clock, the transfer rate is the division ratio selected by
the internal synchronous clock selection bits. Any one of f(XIN)/4, f(XIN)/8, f(XIN)/16, f(XIN)/32,
f(XIN)/64, f(XIN)/128 or f(XIN)/256 can be selected by the internal synchronous clock selection bits.
When selecting an external clock as the transfer clock, the transfer rate is the frequency of the clock
input to the CLK pin.
(3) Automatic transfer serial I/O mode
Clock synchronous communication, which does not depend on the CPU, can be continuously per-
formed up to 256 bytes.
(4) Selection function
The following selection functions can be applied to Serial I/O2.
(a) SSTB2 output (for selecting internal synchronous clock)
STB function invalid: SSTB2 output pin is used as a programmable I/O pin.
STB function valid: SSTB2 output pin functions as SSTB2 or SSTB2 output.
(b) SBUSY2 input/output
SBUSY2 input/output function invalid: SBUSY2 pin is used as a programmable I/O pin.
SBUSY2 input/output function valid: SBUSY2 pin functions as input/output of SBUSY2 or SBUSY2.
(c) SRDY2 input/output
SRDY2 input/output function invalid: SRDY2 pin is used as a programmable I/O pin.
SRDY2 input/output function valid: SRDY2 pin functions as input/output of SRDY2 or SRDY2.
(d) SOUT2 P-channel output disable (invalid for P94 as I/O port)
The SOUT2 output pin can be switched between C-MOS 3 state and N-channel open-drain when in
the 8-bit or the automatic transfer serial I/O mode. The mode is selected by the serial transfer select
bits.
(e) LSB first/MSB first
This function switches the starting bit for the transmission/reception; either bit 0 or bit 7. The following
two types can be selected with the transfer direction select bit:
LSB first: transmission/reception begins with from bit 0.
MSB first: transmission/reception begins with from bit 7.