Transmit Operation - NEC V850ES/KE1+ User Manual

14.5.2 Transmit operation

When the ASIMn.UARTEn bit is set to 1, a high level is output from the TXDn pin.
Then, when the ASIMn.TXEn bit is set to 1, transmission is enabled, and the transmit operation is started by writing
transmit data to the TXBn register.
(1) Transmission enabled state
This state is set by the TXEn bit.
• TXEn bit = 1: Transmission enabled state
• TXEn bit = 0: Transmission disabled state
Since UARTn 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.
(2) Starting a transmit operation
In the transmission enabled state, a transmit operation is started by writing transmit data to the TXBn register.
When a transmit operation is started, the data in the TXBn register is transferred to the transmit shift register.
Then, the transmit shift register outputs data to the TXDn pin (the transmit data is transferred sequentially
starting with the start bit). The start bit, parity bit, and stop bits are added automatically.
(3) Transmission interrupt
When the transmit shift register becomes empty, a transmission completion interrupt request signal (INTSTn)
is generated. The timing for generating the INTSTn signal differs according to the specification of the stop bit
length. The INTSTn signal 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 TXBn register, the transmit operation is
suspended.
Caution Normally, when the transmit shift register becomes empty, the INTSTn signal is generated.
However, the INTSTn signal is not generated if the transmit shift register becomes empty
due to reset.
CHAPTER 14 ASYNCHRONOUS SERIAL INTERFACE (UART)
User's Manual U16896EJ2V0UD
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