
APPLICATION
2.5 Serial I/O1
3820 GROUP USER’S MANUAL
2–109
I
Receive operation in the clock synchronous mode
Receive operation in the clock synchronous mode is described below.
G
Start of receive operation
A receive operation is started by writing the following data into the receive buffer register (address
0018
16
) in the receive enable state.
8
1
Transmit data in the full duplex data transfer mode
Arbitrary dummy data in the half duplex data transfer mode
G
Receive operation
Each 1-bit data is read into the receive shift
register from the P4
4
/RxD pin in synchroni-
zation with the rising of the shift clocks.
The data enters first into the most significant
bit of the receive shift register. Each time 1-
bit data is received, the data of the receive
shift register is shifted by 1 bit toward the
least significant bit.
When 1-byte data has been input into the
receive shift register, the data of the receive
shift register is transferred to the receive buffer
register (address 0018
16
).
8
2
When a data transfer to the receive buffer
register is completed, the receive buffer full
flag (bit 1) of the serial I/O1 status register
(address 0019
16
) is set to “1,”
8
3
 a serial I/O1
receive interrupt request occurs.
8
1: Initialization of register or others for a re-
ceive operation. Refer to 
“2.5.4 Register
setting example.”
8
2: When data remains without reading out the data of the receive buffer register (the receive buffer
full flag is “1”) and yet all the receive data has been input to the receive shift register, the overrun
error flag of the serial I/O1 status register is set to “1.” At this time, the data of the receive shift
register is not transferred to the receive buffer register, but the former data of the receive buffer
register is held.
8
3: The receive buffer full flag is cleared to “0” by reading out the receive buffer register.
Receive shift register
P4
4
/RxD
D
1
b0
D
0
Receive shift register
b0
D
4
P4
4
/RxD
D
3
D
0
D
1
D
2
Transfer receive data
[Address 18
16
]
Receive buffer register
Receive shift register
D
7
D
4
D
5
D
6
Serial I/O1 status 
register
[Address 19
16
]
b1
0
1
D
3
D
0
D
1
D
2