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CHAPTER 9 8-BIT SERIAL I/O
9.1 Overview of 8-bit Serial I/O
The 8-bit serial I/O function is the serial transfer of 8-bit data, synchronized with the
shift clock. The shift clock can be selected from one external and three internal clocks.
The data shift direction can be selected as either LSB first or MSB first.
■ Serial I/O function
The 8-bit serial I/O function is the serial input and output of 8-bit data, synchronized with the shift clock.
• The serial I/O converts 8-bit parallel data to serial and outputs the serial data. Similarly, the serial I/O
converts input serial data to parallel and stores the data.
• One shift clock can be selected from one external and three internal clocks.
• The serial I/O can control input and output of the shift clock and can output the internal shift clock.
• The data shift direction (transfer direction) can be selected as either LSB first or MSB first.
Table 9.1-1 Shift clock cycle and transfer speed
Shift clock Clock (cycle) Frequency (Hz)
Transfer speed (F
CH
= 5 MHz)
Internal shift clock (output) 2 t
inst
1/(2 t
inst
)
625 kbps
8 t
inst
1/(8 t
inst
)
156 kbps
32 t
inst
1/(32 t
inst
)
39 kbps
External shift clock (input) 2 t
inst
or more 1/(2 t
inst
) or less
DC to 625 kbps
F
CH
: main clock oscillation frequency
t
inst
: Instruction cycle (1 instruction cycle = 4/F
CH
).