M38203M4 Datasheet, PDF (226/344 Pages) Mitsubishi Electric Semiconductor – 8-BIT SINGLE-CHIP MICROCOMPUTER

APPLICATION
2.5 Serial I/O1
(4) For disabling transmission after completion of 1-byte data transmission
As a means to know the completion of data transmission, a reference to the transmit shift register shift
completion flag (TSC flag) is available in the 3820 group.
The TSC flag is cleared to “0” during data transmission. Upon the completion of data transmission,
this flag is set to “1.” Accordingly, after confirming that the TSC flag is set to “1,” disable transmission.
The transmission can thus be terminated after 1-byte transmission. However, the TSC flag is set to
“1” even when the serial I/O1 enable bit is set to “1” (serial I/O1 enabled). After that, it is not cleared
to “0” until transmission is started by generating a shift clock. For this reason, if transmission is
disabled by referring to the TSC flag at this time, data is not transmitted. After the transmission is
started, refer to the TSC flag.
(5) When the P45/TxD pin is used as an N-channel open-drain output
Bit 4 of the UART control register (address 001B16) is the P45/TxD P-channel output disable bit. The
bit 4 is valid in an ordinary port, in the clock synchronous mode, or in the UART mode.
When this bit is “0,” the ordinary CMOS output is selected. When the bit is “1,” the N-channel open-
drain output is selected.
However, do not apply to the P45/TXD a voltage of VCC + 0.3 V or more even when it is used as a
serial I/O1 function pin of the N-channel open-drain output.
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3820 GROUP USER’S MANUAL