M38203M4 Datasheet, PDF (192/344 Pages) Mitsubishi Electric Semiconductor – 8-BIT SINGLE-CHIP MICROCOMPUTER

APPLICATION
2.5 Serial I/O1
sTransmit operation in the clock synchronous mode
Transmit operation in the clock synchronous mode is described below.
qStart of transmit operation
A transmit operation is started by writing transmit data into the transmit buffer register (address
001816) in the transmit enable state.^V1
qTransmit operation
ŒBy writing transmit data into the transmit buffer
register, the transmit buffer empty flag (bit 0)
of the serial I/O1 status register (address
001916) is cleared to “0.”
The transmit data written in the transmit buffer
register is transferred to the transmit shift
register.^V2
ŽWhen a data transfer from the transmit buffer
register to the transmit shift register is com-
pleted, the transmit buffer empty flag is
set to “1.”^V3
The transmit data transferred to the transmit
shift register is output from the P45/TxD pin
in synchronization with the falling of the shift
clocks.
The data is output from the least significant
bit of the transmit shift register. Each time 1-
bit data is output, the data of the transmit
shift register is shifted by 1 bit toward the
least significant bit.
Data bus
[Address 1816]
Write transmit data
Transmit buffer register
b0
Serial I/O1 status
1
register
[Address 1916]
0
Transmit buffer register
Transfer transmit data
Transmit shift register
Serial I/O1 status
0
register
[Address 1916]
1
b0
b0
D7 D6 D5 D4 D3 D2 D1
Transmit shift register
D0
P45/TxD
b0
D7 D6 D5 D4 D3 D2
Transmit shift register
D1
P45/TxD
V1: Initialization of register or others for a trans-
mit operation. Refer to “2.5.4 Register set-
ting example.”
V2: When the transmit interrupt source selec-
tion bit (bit 3) of the serial I/O1 control
register (address 001A16) is set to “0,” a
serial I/O1 transmit interrupt request occurs
immediately after transfer in . When this
bit is set to “1,” a transmit interrupt re-
quest occurs at the time of ’.
V3: While the transmit buffer empty flag is “1,” it is possible to write the next transmit data into the
transmit/receive buffer register.
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3820 GROUP USER’S MANUAL