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Rev. 2.50
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Rev. 2.50
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HT66F20/HT66F30/HT66F40/HT66F50/HT66F60
HT66FU30/HT66FU40/HT66FU50/HT66FU60
A/D Flash MCU with EEPROM
HT66F20/HT66F30/HT66F40/HT66F50/HT66F60
HT66FU30/HT66FU40/HT66FU50/HT66FU60
A/D Flash MCU with EEPROM
Managing Receiver Errors
Several types of reception errors can occur within the UART module, the following section describes
the various types and how they are managed by the UART.
• Overrun Error – OERR flag
The RXR register is composed of a four byte deep FIFO data buffer, where four bytes can be held
in the FIFO register, while a 5th byte can continue to be received. Before the 5th byte has been
entirely shifted in, the data should be read from the RXR register. If this is not done, the overrun
error flag OERR will be consequently indicated.
In the event of an overrun error occurring, the following will happen:
♦
The OERR flag in the USR register will be set.
♦
The RXR contents will not be lost.
♦
The shift register will be overwritten.
♦
An interrupt will be generated if the RIE bit is set.
The OERR flag can be cleared by an access to the USR register followed by a read to the RXR
register.
• Noise Error – NF flag
Over-sampling is used for data recovery to identify valid incoming data and noise. If noise is
detected within a frame, the following will occur:
♦
The read only noise flag, NF, in the USR register will be set on the rising edge of the RXIF bit.
♦
Data will be transferred from the shift register to the RXR register.
♦
No interrupt will be generated. However this bit rises at the same time as the RXIF bit which
itself generates an interrupt.
Note that the NF flag is reset by a USR register read operation followed by an RXR register read
operation.
• Framing Error – FERR flag
The read only framing error flag, FERR, in the USR register, is set if a zero is detected instead of
stop bits. If two stop bits are selected, both stop bits must be high. Otherwise the FERR flag will
be set. The FERR flag is buffered along with the received data and is cleared in any reset.
• Parity Error – PERR flag
The read only parity error flag, PERR, in the USR register, is set if the parity of the received
word is incorrect. This error flag is only applicable if the parity function is enabled, PREN=1, and
if the parity type, odd or even, is selected. The read only PERR flag is buffered along with the
received data bytes. It is cleared on any reset, it should be noted that the FERR and PERR flags
are buffered along with the corresponding word and should be read before reading the data word.