Rohm LAPIS SEMICONDUCTOR ML620Q503, User Manual

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ML620Q503/Q504 User's Manual
Chapter 13 UART
FEUL620Q504 13–14
13.3.4 Transmit Operation
Transmission is started by setting the U0EN bit of the UART0 control register (UA0CON) to "1" and set transfer
data to UA1BUF. The order of UA0EN setting and UA1BUF setting does not matter.
Figure 13-5 shows the operation timing for transmission.
When the U0EN bit is set to "1" (

), the baud rate generator generates an internal transfer clock of the baud rate
set and starts transmit operation.
The start bit is output to the TXD pin by the falling edge of the internal transfer clock (

). Subsequently, the
transmitted data, a parity bit, and a stop bit are output.
When the start bit is output (

), a UART0 interrupt is requested. In the UART0 interrupt routine, the next data
to be transmitted is written to the transmit buffer (UA1BUF).
When the next data to be transmitted is written to the transmit buffer (UA1BUF), the transmit buffer status flag
(U1FUL) is set to "1" (

) and a UART transmission interrupt is requested on the falling edge of the internal
transfer clock (

) after transmission of the stop bit. At this time if the UART transmission interrupt routine is
terminated without writing the next data to the transmit buffer, the U1FUL bit is not set to "1" (

). The transmit
operation stops when the stop bit is sent, the U1EN bit is reset to "0", and the UART transmission interrupt is
requested.
The valid period for the next transmit data to be written to the transmit buffer is from the generation of an
interrupt to the termination of stop bit transmission. (

)