Atmel ARM-Based Evaluation Kit AT91SAM9N12-EK AT91SAM9N12-EK Data Sheet
Product codes
AT91SAM9N12-EK
849
SAM9N12/SAM9CN11/SAM9CN12 [DATASHEET]
11063K–ATARM–05-Nov-13
41.5.3.3 Transmitter Control
When the transmitter is enabled, the bit TXRDY (Transmitter Ready) is set in the status register UART_SR. The
transmission starts when the programmer writes in the Transmit Holding Register (UART_THR), and after the written
character is transferred from UART_THR to the Shift Register. The TXRDY bit remains high until a second character is
written in UART_THR. As soon as the first character is completed, the last character written in UART_THR is transferred
into the shift register and TXRDY rises again, showing that the holding register is empty.
transmission starts when the programmer writes in the Transmit Holding Register (UART_THR), and after the written
character is transferred from UART_THR to the Shift Register. The TXRDY bit remains high until a second character is
written in UART_THR. As soon as the first character is completed, the last character written in UART_THR is transferred
into the shift register and TXRDY rises again, showing that the holding register is empty.
When both the Shift Register and UART_THR are empty, i.e., all the characters written in UART_THR have been
processed, the TXEMPTY bit rises after the last stop bit has been completed.
processed, the TXEMPTY bit rises after the last stop bit has been completed.
Figure 41-10. Transmitter Control
41.5.4 DMA
Support
Both the receiver and the transmitter of the UART are connected to a DMA Controller (DMAC) channel.
The DMA Controller channels are programmed via registers that are mapped within the DMAC user interface.
41.5.5 Test
Modes
The UART supports three test modes. These modes of operation are programmed by using the field CHMODE (Channel
Mode) in the mode register (UART_MR).
Mode) in the mode register (UART_MR).
The Automatic Echo mode allows bit-by-bit retransmission. When a bit is received on the URXD line, it is sent to the
UTXD line. The transmitter operates normally, but has no effect on the UTXD line.
UTXD line. The transmitter operates normally, but has no effect on the UTXD line.
The Local Loopback mode allows the transmitted characters to be received. UTXD and URXD pins are not used and the
output of the transmitter is internally connected to the input of the receiver. The URXD pin level has no effect and the
UTXD line is held high, as in idle state.
output of the transmitter is internally connected to the input of the receiver. The URXD pin level has no effect and the
UTXD line is held high, as in idle state.
The Remote Loopback mode directly connects the URXD pin to the UTXD line. The transmitter and the receiver are
disabled and have no effect. This mode allows a bit-by-bit retransmission.
disabled and have no effect. This mode allows a bit-by-bit retransmission.
UART_THR
Shift Register
UTXD
TXRDY
TXEMPTY
Data 0
Data 1
Data 0
Data 0
Data 1
Data 1
S
S
P
P
Write Data 0
in UART_THR
Write Data 1
in UART_THR
stop
stop