Rev. 1.60
182
August 20, 2019
Rev. 1.60
183
August 20, 2019
BS66F340/BS66F350/BS66F360/BS66F370
Touch A/D Flash MCU with LED Driver
BS66F340/BS66F350/BS66F360/BS66F370
Touch A/D Flash MCU with LED Driver
Idle Status
When the receiver is reading data, which means it will be in between the detection of a start bit and
the reading of a stop bit, the receiver status flag in the USR register, otherwise known as the RIDLE
flag, will have a zero value. In between the reception of a stop bit and the detection of the next start
bit, the RIDLE flag will have a high value, which indicates the receiver is in an idle condition.
Receiver Interrupt
The read only receive interrupt flag, RXIF, in the USR register is set by an edge generated by the
receiver. An interrupt is generated if RIE=1, when a word is transferred from the Receive Shift Register,
RSR, to the Receive Data Register, RXR. An overrun error can also generate an interrupt if RIE=1.
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
The RXR register is composed of a two byte deep FIFO data buffer, where two bytes can be held in
the FIFO register, while a 3
th
byte can continue to be received. Before the 3
th
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
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
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
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.
