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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(X
IN
)/4, f(X
IN
)/8, f(X
IN
)/16, f(X
IN
)/32,
f(X
IN
)/64, f(X
IN
)/128 or f(X
IN
)/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) S
STB2
output (for selecting internal synchronous clock)
STB function invalid: S
STB2
output pin is used as a programmable I/O pin.
STB function valid: S
STB2
output pin functions as S
STB2
or S
STB2
output.
(b) S
BUSY2
input/output
S
BUSY2
input/output function invalid: S
BUSY2
pin is used as a programmable I/O pin.
S
BUSY2
input/output function valid: S
BUSY2
pin functions as input/output of S
BUSY2
or S
BUSY2
.
(c) S
RDY2
input/output
S
RDY2
input/output function invalid: S
RDY2
pin is used as a programmable I/O pin.
S
RDY2
input/output function valid: S
RDY2
pin functions as input/output of S
RDY2
or S
RDY2
.
(d) S
OUT2
P-channel output disable (invalid for P9
4
as I/O port)
The S
OUT2
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.