HD404019RFS datasheet(21/65 Pages) RENESAS

21 / 65 page

HD404019R Series

Serial Interface

The serial interface is used to transmit/receive 8-bit data serially. It consists of the serial data register, the

serial mode register, the octal counter, and the multiplexer as illustrated in figure 9. Pin R4

0/SCK and the

transmit clock signal are controlled by the serial mode register. The contents of the serial data register can

be written into or read out by software. The data in the serial data register can be shifted synchronously

with the transmit clock signal.

The STS instruction initiates serial interface operations and resets the octal counter to $0. The counter starts

to count at the falling edge of the transmit clock (

SCK) signal and increments by one at the rising edge of

SCK. When the octal counter is reset to $0 after eight transmit clock signals, or a transmit/receive operation

is discontinued, the serial interrupt request flag will be set.

System

clock

Prescaler (11 bits)

Serial MPX

÷ 2

MPX

SMR (4 bits)

Serial mode register

R40/SCK

port

SCK

OC (3 bits)

Octal counter

IFS

SROF

Serial

interface

interrupt

request flag

Internal bus line (S1)

SR (8 bits)

Serial data register

SCK

PMR (4 bits)

Port mode register

R41/SI

port

R42/SO

port

Internal bus line (S2)

Internal bus-line (S2)

Figure 9 Serial Interface Block Diagram

Serial Mode Register (SMR: $005): The 4-bit write-only serial mode register controls the R4

0/SCK pin,

prescaler divide ratio, and transmit clock source as shown in table 7.

The write signal to the serial mode register controls the operating state of the serial interface.

The write signal to the serial mode register stops the serial data register and octal counter from accepting

the transmit clock, and it also resets the octal counter to $0 simultaneously. Therefore, when the serial

interface is in the transfer state, the write signal causes the serial mode register to cease the data transmit

and to set the serial interrupt request flag.

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