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Timing by which the first interrupt occurs to start transmission

Latest Updated: 03/21/2017

Question:

I would like to use transmission interrupts with UART to execute asynchronous half-duplex communications.
What is the timing by which the first interrupt occurs in order to start transmission?

Answer:

UART's interrupt is a transmission completion interrupt, so it occurs at the stop bit's timing in the transmitted data.

Description
In almost all devices, the interrupt related to the transmission for microcontroller-embedded UART is a "transmission completion" interrupt.
When using UARTAn in the V850ES/SG2 or V850ES/SJ2 (hereafter referred to simply as the V850ES/SJ2), this is a "transmission enable" interrupt.

In either case, just setting transmit as enabled does not trigger an interrupt.
When the first data is written, an interrupt occurs when transmission of that data is completed (in the V850ES/SJ2, this interrupt occurs when data has been transferred to the transmit shift register).

The second and subsequent bytes of transmit data are written via this interrupt timing.
Note with caution that the processing differs between the first bytes of data to be transmitted and the second and subsequent bytes.

The V850ES/ME2 includes a FIFO, so a special operation is used for transmit-related interrupts (this operation will not be described here).
Suitable Products
V850 Family