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7220 Group User’s Manual

FUNCTIONAL DESCRIPTION

2.7 Serial I/O

Bit 0

2.7.2 Serial I/O register (address 00DD16)

The serial I/O register is serial-parallel conversion register used for data transfer. This register consists of

8-bit and can be used as both transmit and receive register.

Serial I/O register is assigned to address 00DD16.

Although data transfer is performed bit by bit, it is possible to specify whether the data is transferred

beginning with most-significant-bit (MSB) or least-significant-bit (LSB) by using bit 5 of the serial I/O mode

(1)

When bit 5 of the serial I/O mode register is “0”

q Receive: Data is received bit by bit beginning with the MSB (bit 7) of the serial I/O register.

q Transmit: Data is transmitted bit by bit beginning with the LSB (bit 0) of the serial I/O register.

(2)

When bit 5 of the serial I/O mode register is “1”

q Receive: Data is received bit by bit beginning with the LSB (bit 0) of the serial I/O register.

q Transmit: Data is transmitted bit by bit beginning with the MSB (bit 7) of the serial I/O register.

2.7.3 Clock source generating circuit

The clock source generating circuit can select oscillation frequency divided by 4, 16, 32, and 64 as the

internal clock. Also, it can select an external clock (the external clock is selected immediately after reset).

Bit 2 of the serial I/O mode register specifies internal clock or external clock. When bit 2 of the serial

I/O mode register is set to “0,” an external clock is

selected, when “1,” an internal clock is selected.

When selecting an internal clock, set the division

of oscillation frequency by bits 0 and 1 of the serial

I/O mode register.

q Oscillation frequency divided by 4:

set both bits 1 and 0 to “0.”

q Oscillation frequency divided by 16:

set bit 1 = “0” and bit 0 = “1.”

q Oscillation frequency divided by 32:

set bit 1 = “1” and bit 0 = “0.”

q Oscillation frequency divided by 64:

set both bit 1 and 0 to “1.”

The contents of bits 0 and 1 of the serial I/O mode register are invalid, when selecting an external clock.

2.7.4 Serial input/output common transmission/reception mode

Pin P21/SOUT can also be used as the serial I/O data input pin when the serial input pin selection bit (bit

6 of the serial I/O mode register; address 00DC16) is set to “1.” (It is not necessary to set the corresponding

bit of port P2 direction register to input mode.)

With this function, pin P22/SIN can also be used as general-purpose input port P22.

Serial I/O clock

External clock

Internal

clock

Serial I/O mode register

Bit 2

Bit 1

Table 2.7.1 Clock source selection

f(XIN)/4

f(XIN)/16

f(XIN)/32

f(XIN)/64

0 or 1 (Invalid)

Fig. 2.7.3 Serial input/output common transfer mode block diagram

Serial I/O register (8)

Clock

Transmit mode

Receive mode

Port P22 data

SM6

P22/SIN

P21/SOUT

P20/SCLK

“1”

“0”

Input or output

SM: Serial I/O register

Note: To start receiving, set “FF16” to the serial I/O register

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