17.3.5.5 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 regis-
ters.
17.3.5.6 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 detec-
ted as a start frame.
17.3.5.7 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 re-
ceiver 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 program-
mable 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 DeepSleep, 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.
EFM32JG1 Reference Manual
LEUART - Low Energy Universal Asynchronous Receiver/Transmitter
silabs.com
| Smart. Connected. Energy-friendly.
Preliminary Rev. 0.6 | 549