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7220 Group User’s Manual

FUNCTIONAL DESCRIPTION

2.7 Serial I/O

Fig. 2.7.5 Serial I/O register when transmitting (when SM5 = “0”)

2.7.6 Serial I/O data transmit method (when an external clock is selected)

(1)

Initialization

First, set the serial I/O mode register (address 00DC16) as follows.

Select the synchronous clock (SM2 = “0”).

Set P20 as pin SCLK (SM3 = “1”). Since the serial I/O port selection bit (SM3) is also used for the

setting pin SOUT, port P21 is automatically becomes the S OUT pin.

Note: It is not necessary to set pin P22/SIN as pin SIN when transmitting. It can be used as general-

purpose input pin.

(2)

Transmit enable state

When transmit data are written to the serial I/O register, the serial I/O counter is set to “0716” and

transmit is enabled.

(3)

Transmit operation

When transmit is enabled (the serial I/O counter value = “0716”), simultaneously, the data of the serial

I/O register is transmitted from pin P21/SOUT in synchronization with a falling edge of the transfer

clock.

Transmission is performed according to bit 5 (SM5) of the serial I/O mode register:

When SM5 is set to “0,” data is transmitted from LSB (bit 0) of the register and shifted to the right

(to low-order bit) every time new data is transmitted.

When SM5 is set to “1,” data is transmitted from MSB (bit 7) of the register and shifted to the left

(to high-order bit) every time new data is transmitted.

When all 8-bit data have been transmitted, the serial I/O interrupt request bit (bit 2) of the interrupt

request register 2 (address 00FD 16) is set to “1.”

Pin P21/SOUT will be in after transmit operation has been completed.

Note: On programming, note that the serial I/O counter is set even by writing to the serial I/O register

with bit management instructions, such as SEB and CLB.

Transfer clock

Serial I/O register

MSB

LSB

D7 D6 D5 D4 D3 D2 D1 D0

D7 D6 D5 D4 D3 D2 D1

D7 D6 D5 D4 D3 D2

D7 D6 D5 D4

When transmitting

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