13 14 15 16 1
2
3
4
5
6
7
8
9 10 11
1/2 stop bit
7
8
1
2
3
4
5
6
13
7
12
OVS
= 0
OVS
= 1
14 15 16
8
P
NAK or stop
17 18 X
9
10
X
X
X
X X X
X
Stop
1
2
3
4
5
6
7
OVS
= 2
1
2
3
4
5
x
OVS
= 3
8
x
6
4
Figure 16.17. USART SmartCard Stop Bit Sampling
For communication with a SmartCard, a clock signal needs to be generated for the card. This clock output can be generated using one
of the timers. See the ISO 7816 specification for more info on this clock signal.
SmartCard T1 mode is also supported. The T1 frame format used is the same as the asynchronous frame format with parity bit enabled
and one stop bit. The USART must then be configured to operate in asynchronous half duplex mode.
16.3.3 Synchronous Operation
Most of the features in asynchronous mode are available in synchronous mode. Multi-processor mode can be enabled for 9-bit frames,
loopback is available and collision detection can be performed.
16.3.3.1 Frame Format
The frames used in synchronous mode need no start and stop bits since a single clock is available to all parts participating in the com-
munication. Parity bits cannot be used in synchronous mode.
The USART supports frame lengths of 4 to 16 bits per frame. Larger frames can be simulated by transmitting multiple smaller frames,
i.e. a 22 bit frame can be sent using two 11-bit frames, and a 21 bit frame can be generated by transmitting three 7-bit frames. The
number of bits in a frame is set using DATABITS in USARTn_FRAME.
The frames in synchronous mode are by default transmitted with the least significant bit first like in asynchronous mode. The bit-order
can be reversed by setting MSBF in USARTn_CTRL.
The frame format used by the transmitter can be inverted by setting TXINV in USARTn_CTRL, and the format expected by the receiver
can be inverted by setting RXINV, also in USARTn_CTRL.
EFM32JG1 Reference Manual
USART - Universal Synchronous Asynchronous Receiver/Transmitter
silabs.com
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