7220 Datasheet, PDF (70/303 Pages) Renesas Technology Corp – 8-BIT SINGLE-CHIP MICROCOMPUTER

FUNCTIONAL DESCRIPTION
2.7 Serial I/O
2.7.5 Serial I/O data receive method (when an internal clock is selected)
(1) Initialization
First, set the serial I/O mode register (address 00DC16) as follows.
Œ Select the synchronous clock (SM2 = “1,” SM1, SM0).
 Set P20 as pin SCLK (SM3 = “1”). Pin P21/SOUT is not used when receiving serial data. However,
since the serial I/O port selection bit (SM3) is also used for setting pin SOUT, port P21 is automatically
set as pin SOUT and loses its general-purpose I/O port function.
Ž Select the serial input pin by the serial input pin selection bit (SM6). When SM6 = “0,” signal is
input from pin P22/SIN; when SM6 = “1,” signal is input from pin P21/SOUT. When pin P22/SIN is a
input pin, set the port P2 direction register to input mode (“0”). For pins P20/SCLK and P21/SOUT, the
corresponding bits of the port P2 direction register are automatically set by setting the serial I/O
mode register.
(2) Receive enable state
After the above setting have been made, write “FF16” to the serial I/O register (address 00DD16). The
serial I/O counter is then set to “0716” during the write cycle and receive is enabled.
(3) Receive operation
The data from the serial I/O data input pins (SOUT or SIN) is received one bit at a time into the serial
I/O register in synchronization with rising edges of the transfer clock.
Receive operation is performed according to bit 5 (SM5) of the serial I/O mode register:
Œ When SM5 is set to “0,” data is received from MSB (bit 7) of the register and shifted to the right
(to low-order bit) every time new data is received.
 When SM5 is set to “1,” data is received from LSB (bit 0) of the register and shifted to the left (to
high-order bit) every time new data is received.
When all 8-bit data have been received, the serial I/O interrupt request bit (bit 2) of the interrupt
request register 2 (address 00FD16) is set to “1.”
MSB
LSB
When receiving
D0
D1 D0
Transfer clock
D2 D1 D0
•
•
•
D7 D6 D5 D4 D3 D2 D1 D0
Serial I/O register
Note: To start receiving, set “FF16” to the serial I/O register.
Fig. 2.7.4 Serial I/O register when receiving (when SM5 = “0”)
7220 Group User’s Manual
2-43