
CHAPTER 13 PERIPHERAL HARDWARE
135
13.3 SERIAL INTERFACE (SIO)
The serial interfaces of the
μ
PD17120 subseries consists of a shift register (SIOSFR, 8 bits), serial mode register,
and serial clock counter. It is used for serial data input/output.
13.3.1 Functions of the Serial Interface
This serial interface provides three signal lines: serial clock input pin (SCK), serial data output pin (SO), and serial
data input pin (SI). It allows 8 bits to be sent or received in synchronization with clocks. It can be connected to
peripheral input/output devices using any method with a mode compatible to that used by the
μ
PD7500 or 75X series.
(1) Serial clock
Three types of internal clocks and one type of external clock can be selected. If an internal clock is selected
as a serial clock, it is automatically output to the P0D
0
/SCK pin.
Table 13-2. List of Serial Clock
SIOCK1
SIOCK0
Serial clock to be selected
0
0
External clock from the SCK pin
0
1
f
X
/16
1
0
f
X
/128
1
1
f
X
/1024
(2) Transmission operation
By setting (to 1) SIOEN, each pin of port 0D (P0D
0
/SCK, P0D
1
/SO, P0D
2
/SI) functions as a pin for serial
interfacing. At this time, if SIOTS is set (to 1), the operation is started synchronously with the falling edge
of the serial clock. Also, setting SIOTS will result in automatically clearing IRQSIO.
The transfer is started from the most significant bit of the shift register synchronously with the falling edge
of the serial clock. And, the information on the SI pin is stored in the shift register from the most significant
bit, synchronously with the rising edge of the clock.
If the 8-bit data transfer is terminated, SIOTS is automatically cleared and IRQSIO is set.
Remark
Serial transmission starts only from the most significant bit of the shift register contents. It is not
possible to transmit from the least significant bit. SI pin status is always stored in the shift register
in synchronization with the rising edge of the serial clock.