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2014-07-02 - Gecko Family - d0001_Rev1.30
250
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• Can use a high frequency clock source for even higher baud rates
• Configurable number of data bits: 8 or 9 (plus parity bit, if enabled)
• Configurable parity: off, even or odd
• HW parity bit generation and check
• Configurable number of stop bits, 1 or 2
• Capable of sleep-mode wake-up on received frame
• Either wake-up on any received byte or
• Wake up only on specified start and signal frames
• Supports transmission and reception in EM0, EM1 and EM2 with
• Full DMA support
• Specified start-byte can start reception automatically
• IrDA modulator (pulse generator, pulse extender)
• Multi-processor mode
• Loopback mode
• Half duplex communication
• Communication debugging
18.3 Functional Description
An overview of the LEUART module is shown in Figure 18.1 (p. 250) .
Figure 18.1. LEUART Overview
18.3.1 Frame Format
The frame format used by the LEUART consists of a set of data bits in addition to bits for synchronization
and optionally a parity bit for error checking. A frame starts with one start-bit (S), where the line is driven
low for one bit-period. This signals the start of a frame, and is used for synchronization. Following the
start bit are 8 or 9 data bits and an optional parity bit. The data is transmitted with the least significant
bit first. Finally, a number of stop-bits, where the line is driven high, end the frame. The frame format
is shown in Figure 18.2 (p. 250) .
Figure 18.2. LEUART Asynchronous Frame Format
S
0
1
2
3
4
5
6
7
[8]
[P]
St op
St art or idle
St op or idle
Fram e
The number of data bits in a frame is set by DATABITS in LEUARTn_CTRL, and the number of stop-bits
is set by STOPBITS in LEUARTn_CTRL. Whether or not a parity bit should be included, and whether
it should be even or odd is defined by PARITY in LEUARTn_CTRL. For communication to be possible,
all parties of an asynchronous transfer must agree on the frame format being used.
The frame format used by the LEUART can be inverted by setting INV in LEUARTn_CTRL. This affects
the entire frame, resulting in a low idle state, a high start-bit, inverted data and parity bits, and low stop-
bits. INV should only be changed while the receiver is disabled.
18.3.1.1 Parity Bit Calculation and Handling
Hardware automatically inserts parity bits into outgoing frames and checks the parity bits of incoming
frames. The possible parity modes are defined in Table 18.1 (p. 251) . When even parity is chosen,
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