19.3.5.8 Multi-Processor Mode
To simplify communication between multiple processors and maintain compatibility with the USART, the LEUART supports a multi-pro-
cessor mode. In this mode the 9th data bit in each frame is used to indicate whether the content of the remaining 8 bits is data or an
address.
When multi-processor mode is enabled, an incoming 9-bit frame with the 9th bit equal to the value of MPAB in LEUARTn_CTRL is
identified as an address frame. When an address frame is detected, the MPAF interrupt flag in LEUARTn_IF is set, and the address
frame is loaded into the receive register. This happens regardless of the value of RXBLOCK in LEUARTn_STATUS.
Multi-processor mode is enabled by setting MPM in LEUARTn_CTRL. The mode can be used in buses with multiple slaves, allowing
the slaves to be addressed using the special address frames. An addressed slave, which was previously blocking reception using
RXBLOCK, would then unblock reception, receive a message from the bus master, and then block reception again, waiting for the next
message. See the USART for a more detailed example.
Note:
The programmable start frame functionality can be used for automatic address matching, enabling reception on a correctly configured
incoming frame.
An address frame with a parity error or a framing error is not detected as an address frame. The Start, Signal, and address frames
should not be set to match the same frame since each of these uses separate synchronization to the peripherial clock domain.
19.3.6 Loopback
The LEUART receiver samples LEUn_RX by default, and the transmitter drives LEUn_TX by default. This is not the only configuration
however. When LOOPBK in LEUARTn_CTRL is set, the receiver is connected to the LEUn_TX pin as shown in
. This is useful for debugging, as the LEUART can receive the data it transmits, but it is also used to
allow the LEUART to read and write to the same pin, which is required for some half duplex communication modes. In this mode, the
LEUn_TX pin must be enabled as an output in the GPIO.
LEUART
RX
LEUn_RX
TX
LEUn_TX
LOOPBK = 0
µC
LEUART
RX
LEUn_RX
TX
LEUn_TX
LOOPBK = 1
µC
Figure 19.9. LEUART Local Loopback
19.3.7 Half Duplex Communication
When doing full duplex communication, two data links are provided, making it possible for data to be sent and received at the same
time. In half duplex mode, data is only sent in one direction at a time. There are several possible half duplex setups, as described in the
following sections.
Reference Manual
LEUART - Low Energy Universal Asynchronous Receiver/Transmitter
silabs.com
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