Precautions On Using Uart Mode - Mitsubishi 32172 User Manual

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12.9 Precautions on Using UART Mode

• Settings of SIO Transmit/Receive Mode Register and SIO Baud Rate Register
The SIO Transmit/Receive Mode Register and SIO Baud Rate Register and the Transmit Control
Register's BRG count source select bit must always be set when not operating. When transmitting
or receiving data, be sure to check that transmission and/or reception under way has been
completed and clear the transmit and receive enable bits before you set the registers.
• Settings of Baud Rate (BRG) Register
If you selected f(BCLK) with the BRG clock source select bit, make sure the BRG register value you
set is equal to or greater than 7.
The value written to the SIO Baud Rate Register becomes effective beginning with the next period
after the BRG counter finished counting. However, when transmit and receive operations are
disabled, the register value can be changed at the same time you write to the register.
• Transmit/receive operations using DMA
To transmit/receive data in DMA request mode, enable the DMAC to accept transfer requests (by
setting the DMA Mode Register) before you start serial communication.
• About overrun error
If all bits of the next receive data are received in the SIO Receive Shift Register before you read out
the SIO Receive Buffer Register (an overrun error occurs), the receive data is not stored in the
Receive Buffer Register and the Receive Buffer Register retains the previously received data.
Once an overrun error occurs, no receive data is stored in the Receive Buffer Register although
receive operation is continued. To restart reception normally, you need to temporarily clear the
receive enable bit before you restart. This is the only way you can clear the overrun error flag.
12.9 Precautions on Using UART Mode
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SERIAL I/O
Rev.1.0