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SERIAL INTERFACE
12
12-62
32185/32186 Group Hardware Manual
Rev.1.10 REJ09B0235-0110 May 15, 07
12.9 Notes on Using UART Mode
Settings of SIO Transmit/Receive Mode Register and SIO Baud Rate Register
The SIO Transmit/Receive Mode Register, SIO Special Mode Register and SIO Baud Rate
Register and the Transmit Control Register’s BRG count source select bit must always be set when
the serial interface is not operating. If a transmit or receive operation is in progress, wait until the
transmit and receive operations are finished and then clear the transmit and receive enable bits
before making changes.
Settings of Baud Rate Register (SnBAUR)
Writes to the SIO Baud Rate Register take effect in the next cycle after the BRG counter has
finished counting. However, if the register is accessed for write while transmission and reception
are disabled, the written value takes effect at the same time it is written.
Transmission/reception using DMA
To transmit/receive data in DMA request mode, enable the DMAC to accept transfer requests (by
setting the DMA Mode Register) before serial communication starts.
About overrun error
If all bits of the next received data have been set in the SIO Receive Shift Register before reading
out the SIO Receive Buffer Register (i.e., an overrun error occurred), the received data is not stored
in the receive buffer register, with the previous received data retained in it. Once an overrun error
occurs, although a receive operation continues, the subsequent received data is not stored in the
receive buffer register. Before normal receive operation can be restarted, the receive enable bit
must be temporarily cleared. And this is the only way that the overrun error flag can be cleared.
Flags showing the status of UART receive operation
There are following flags that indicate the status of receive operation during UART mode:
SIO Receive Control Register receive status bit
SIO Receive Control Register reception finished bit
SIO Receive Control Register receive error sum bit
SIO Receive Control Register overrun error bit
SIO Receive Control Register parity error bit
SIO Receive Control Register framing error bit
The manner in which the reception finished bit and various error flags are cleared differs depending
on whether an overrun error occurred, as described below.
[When an overrun error did not occur]
Cleared by reading out the lower byte of the receive buffer register or by clearing the receive enable bit.
[When an overrun error occurred]
Cleared by only clearing the receive enable bit.
Switching from general-purpose port to serial interface pin
When switching from general-purpose port to the serial interface pin by the port operation mode
register, the terminal TXDn pin outputs "H" level.
12.9 Notes on Using UART Mode