APPLICATION
2.5 Serial I/O
3825 GROUP USER’S MANUAL
2–108
sReceive operation in the clock synchronous mode
Receive operation in the clock synchronous mode is described below.
qStart of receive operation
A receive operation is started by writing the following data into the receive buffer register (address
001816) in the receive enable state.V1
Transmit data in the full duplex data transfer mode
Arbitrary dummy data in the half duplex data transfer mode
qReceive operation
Each 1-bit data is read into the receive shift
register from the P44/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 001816).V2
When a data transfer to the receive buffer
register is completed, the receive buffer full
flag (bit 1) of the serial I/O status register
(address 001916) is set to “1,”V3 a serial I/O
receive interrupt request occurs.
V1: Initialization of register or others for a re-
ceive operation. Refer to “2.5.4 Register
setting example.”
V2: 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/O 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.
V3: The receive buffer full flag is cleared to “0” by reading out the receive buffer register.
Receive shift register
P44/RxD
D1
b0
D0
Receive shift register
b0
D4
P44/RxD
D3
D0
D1
D2
Transfer receive data
Receive buffer register
Receive shift register
[Address 1816]
D7
D4
D5
D6
Serial I/O status
register
[Address 1916]
b1
0
1
D3
D0
D1
D2