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2.4 Serial I/O

2-40

4513/4514 Group User’s Manual

2.4 Serial I/O

The 4513/4514 Group has a clock-synchronous serial I/O which can be used to transmit and receive 8-bit

data.

This section describes serial I/O functions, related registers, application examples using serial I/O and

notes.

2.4.1 Carrier functions

Serial I/O consists of the serial I/O register SI, serial I/O mode register J1, serial I/O transmit/receive

completion flag SIOF and serial I/O counter.

A clock-synchronous serial I/O uses the shift clock generated by the clock control circuit as a synchronous

clock. Accordingly, the data transmit and receive operations are synchronized with this shift clock.

In transmit operation, data is transmitted bit by bit from the SOUT pin synchronously with the falling edges

of the shift clock.

In receive operation, data is received bit by bit from the SIN pin synchronously with the rising edges of the

shift clock.

Note: 4513/4514 Group only supports LSB-first transmission and reception.

Shift clock

When using the internal clock of 4513/4514 Group as a synchronous clock, eight shift clock pulses

are output from the SCK pin when a transfer operation is started. Also, when using some external

clock as a synchronous clock, the clock that is input from the SCK pin is used as the shift clock.

Data transfer rate (baudrate)

When using the internal clock, the data transfer rate can be determined by selecting the instruction

clock divided by 4 or 8.

When using an external clock, the clock frequency input to the SCK pin determines the data transfer

rate.

Figure 2.4.1 shows the serial I/O block diagram.

Fig. 2.4.1 Serial I/O block diagram

J12

SIOF

J12

J11

J10

J11

J10

MSB

1/4

1/8

P21/SOUT

P22/SIN

P20/SCK

TSIAB

TABSI

SOUT

SIN

SCK

J13

MR3

XIN

Division circuit

(divided by 2)

Internal clock

generation circuit

(divided by 3)

Instruction clock

Serial I/O mode register J1

Serial I/O interrupt

Serial I/O counter (3)

Synchronous

circuit

Serial I/O register SI (8)

LSB

Note: The output structure of SCK and SOUT pins is N-channel open-drain.

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