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FUNCTIONAL DESCRIPTION
2.7 Serial I/O
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 00DC
Select the synchronous clock (SM2 = "0").
Set P2
as pin S
0
setting pin S
Note: It is not necessary to set pin P2
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 "07
transmit is enabled.
(3) Transmit operation
When transmit is enabled (the serial I/O counter value = "07
I/O register is transmitted from pin P2
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
Pin P2
/S
will be in after transmit operation has been completed.
1
OUT
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.
When transmitting
Fig. 2.7.5 Serial I/O register when transmitting (when SM5 = "0")
2-44
(SM3 = "1"). Since the serial I/O port selection bit (SM3) is also used for the
CLK
, port P2
is automatically becomes the S
OUT
1
) is set to "1."
16
Transfer clock
7220 Group User's Manual
) as follows.
16
/S
as pin S
when transmitting. It can be used as general-
2
IN
IN
16
/S
in synchronization with a falling edge of the transfer
1
OUT
MSB
D
D
D
D
7
6
5
D
D
D
7
6
D
D
7
D
Serial I/O register
pin.
OUT
"), simultaneously, the data of the serial
LSB
D
D
D
D
4
3
2
1
0
D
D
D
D
5
4
3
2
1
D
D
D
D
6
5
4
3
2
D
D
D
D
7
6
5
3
4
•
•
•
" and
16
D
0
D
1
D
2
D
7
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