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SUMMARY OF PRECAUTIONS
Appendix 4
Appendix 4-26
32185/32186 Group Hardware Manual
Rev.1.10 REJ09B0235-0110 May 15, 07
Appendix 4.11 Notes on Serial Interface
Switching from general-purpose to serial interface pin
When switching general-purpose to serial interface pin, SCLKOn pin outputs "H" level (For the case of select-
ing internal clock and setting CKPOL bit to "0." When setting CKPOL bit to "1," it outputs "L" level.), and TXDn
pin outputs undefined value. However, when switching general-purpose to serial interface pin with setting TEN
bit of the SIOn transmit control register to "1" (transmit enable), TXDn pin outputs the last bit level of the
previously output serial data.
Appendix 4.11.2 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 SIOn 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 SIOn Baud Rate Register
Writes to the SIOn 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.