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2014-07-02 - Gecko Family - d0001_Rev1.30
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PERR can be accessed by reading the frame from the receive buffer using the LEUARTn_RXDATAX
register.
18.3.5.5 Framing Error and Break Detection
A framing error is the result of a received frame where the stop bit was sampled to a value of 0. This
can be the result of noise and baud rate errors, but can also be the result of a break generated by the
transmitter on purpose.
When a framing error is detected, the framing error bit FERR in the received frame is set. The interrupt
flag FERR in LEUARTn_IF is also set. Frames with framing errors are loaded into the receive buffer
like regular frames.
FERR can be accessed by reading the frame from the receive buffer using the LEUARTn_RXDATAX
or LEUARTn_RXDATAXP registers.
18.3.5.6 Programmable Start Frame
The LEUART can be configured to start receiving data when a special start frame is detected on the input.
This can be useful when operating in low energy modes, allowing other devices to gain the attention of
the LEUART by transmitting a given frame.
When SFUBRX in LEUARTn_CTRL is set, an incoming frame matching the frame defined in
LEUARTn_STARTFRAME will result in RXBLOCK in LEUARTn_STATUS being cleared. This can be
used to enable reception when a specified start frame is detected. If the receiver is enabled and blocked,
i.e. RXENS and RXBLOCK in LEUARTn_STATUS are set, the receiver will receive all incoming frames,
but unless an incoming frame is a start frame it will be discarded and not loaded into the receive buffer.
When a start frame is detected, the block is cleared, and frames received from that point, including the
start frame, are loaded into the receive buffer.
An incoming start frame results in the STARTF interrupt flag in LEUARTn_IF being set, regardless of
the value of SFUBRX in LEUARTn_CTRL. This allows an interrupt to be made when the start frame
is detected.
When 8 data-bit frame formats are used, only the 8 least significant bits of LEUARTn_STARTFRAME
are compared to incoming frames. The full length of LEUARTn_STARTFRAME is used when operating
with frames consisting of 9 data bits.
Note
The receiver must be enabled for start frames to be detected. In addition, a start frame with
a parity error or framing error is not detected as a start frame.
18.3.5.7 Programmable Signal Frame
As well as the configurable start frame, a special signal frame can be specified. When a frame matching
the frame defined in LEUARTn_SIGFRAME is detected by the receiver, the SIGF interrupt flag in
LEUARTn_IF is set. As for start frame detection, the receiver must be enabled for signal frames to be
detected.
One use of the programmable signal frame is to signal the end of a multi-frame message transmitted to
the LEUART. An interrupt will then be triggered when the packet has been completely received, allowing
software to process it. Used in conjunction with the programmable start frame and DMA, this makes it
possible for the LEUART to automatically begin the reception of a packet on a specified start frame,
load the entire packet into memory, and give an interrupt when reception of a packet has completed.
The device can thus wait for data packets in EM2, and only be woken up when a packet has been
completely received.
A signal frame with a parity error or framing error is not detected as a signal frame.
Summary of Contents for EFM32G
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