D17133CS datasheet(150/289 Pages) NEC

150 / 289 page

CHAPTER 13

PERIPHERAL HARDWARE

135

13.3 SERIAL INTERFACE (SIO)

The serial interfaces of the

µPD17120 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

µPD7500 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 P0D0/SCK pin.

Table 13-2. List of Serial Clock

SIOCK1

SIOCK0

Serial clock to be selected

External clock from the SCK pin

fX/16

fX/128

fX/1024

(2) Transmission operation

By setting (to 1) SIOEN, each pin of port 0D (P0D0/SCK, P0D1/SO, P0D2/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.

D17133CS Datasheet(PDF) 150 Page - NEC