CHAPTER 10 SERIAL INTERFACE FUNCTION
User’s Manual U14492EJ3V0UD
427
(2) Transmission operation
When UARTCAE0 bit is set to 1 in the ASIM0 register, a high level is output from the TXD0 pin.
Then, when TXE0 bit is set to 1 in the ASIM0 register, transmission is enabled, and the transmit operation is
started by writing transmit data to transmission buffer register 0 (TXB0).
(a) Transmission enabled state
This state is set by the TXE0 bit in the ASIM0 register.
•
TXE0 = 1: Transmission enabled state
•
TXE0 = 0: Transmission disabled state
Since UART0 does not have a CTS (transmission enabled signal) input pin, a port should be used to
confirm whether the destination is in a reception enabled state.
(b) Transmission operation start
In transmission enabled state, a transmission operation is started by writing transmit data to transmission
buffer register 0 (TXB0). When a transmit operation is started, the data in TXB0 is transferred to
transmission shift register. Then, the transmission shift register outputs data to the TXD0 pin (the
transmit data is transferred sequentially starting with the start bit). The start bit, parity bit, and stop bits
are added automatically.
(c) Transmission interrupt request
When the transmission shift register becomes empty, a transmission completion interrupt request
(INTST0) is generated. The timing for generating the INTST0 interrupt differs according to the
specification of the stop bit length. The INTST0 interrupt is generated at the same time that the last stop
bit is output.
If the data to be transmitted next has not been written to the TXB0 register, the transmit operation is
suspended.
Caution
Normally, when the transmission shift register becomes empty, a transmission
completion interrupt (INTST0) is generated. However, no transmission completion
interrupt (INTST0) is generated if the transmission shift register becomes empty due to
the input of a RESET.
Содержание V850E/IA1 mPD703116
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