SERIAL INTERFACE
12
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32185/32186 Group Hardware Manual
Rev.1.10 REJ09B0235-0110 May 15, 07
12.6.4 Starting UART Transmission
The serial interface starts a transmit operation when all of the following conditions are met after being
initialized.
SIO Transmit Control Register TEN (Transmit Enable) bit is set to "1" (Note 1).
Transmit data is written to the SIO Transmit Buffer Register (transmit buffer empty bit = "0").
Note 1: While the transmit enable bit is cleared to "0," writes to the transmit buffer are ignored. Always be
sure to set the transmit enable bit to "1" before writing to the transmit buffer register.
When transmission starts, the serial interface sends data following the procedure described below.
Transfer the content of the SIO Transmit Buffer Register to the SIO Transmit Shift Register.
Set the transmit buffer empty bit to "1" (Note 2).
Start sending data synchronously with the shift clock.
Note 2: A transmit interrupt request can be generated for reasons that the transmit buffer is empty or
transmission has finished. Also, a DMA transfer request can be generated when the transmit buffer
is empty. No DMA transfer requests can be generated for reasons that transmission has finished.
12.6.5 Successive UART Transmission
Once data has been transferred from the transmit buffer register to the transmit shift register, the next data
can be written to the transmit buffer register even when the serial interface has not finished sending the
previous data. If the next data is written to the transmit buffer before transmission has finished, the previ-
ous and the next data are transmitted successively.
Check the SIO Transmit Control Register’s transmit buffer empty flag to see if data has been transferred
from the transmit buffer register to the transmit shift register.
12.6.6 Processing at End of UART Transmission
When data transmission finishes, the following operation is automatically performed in hardware.
(1) When not transmitting successively
The transmit status bit is cleared to "0."
(2) When transmitting successively
When transmission of the last data in a consecutive data train finishes, the transmit status bit is
cleared to "0."
12.6.7 Transmit Interrupts
(1) Transmit buffer empty interrupt
If the transmit buffer empty interrupt was selected using the SIO Interrupt Request Source Select
Register, a transmit buffer empty interrupt request is generated when data has been transferred from
the transmit buffer register to the transmit shift register. A transmit buffer empty interrupt request is
also generated when the TEN (Transmit Enable) bit is set to "1" (reenabled after being disabled) while
the transmit buffer empty interrupt has been enabled.
12.6 Transmit Operation in UART Mode