SAM9G25_14 Datasheet, PDF (292/1167 Pages) ATMEL Corporation – Atmel | SMART ARM-based Embedded Microprocessor

When both the Shift Register and the DBGU_THR are empty, i.e., all the characters written in DBGU_THR have been
processed, the bit TXEMPTY rises after the last stop bit has been completed.
Figure 24-11.Transmitter Control
DBGU_THR
Data 0
Data 1
Shift Register
Data 0
Data 1
DTXD
S
Data 0
P
stop
S
Data 1
P
stop
TXRDY
TXEMPTY
Write Data 0 Write Data 1
in DBGU_THR in DBGU_THR
24.5.4 DMA Support
Both the receiver and the transmitter of the Debug Unit’s 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.
24.5.5 Test Modes
The Debug Unit supports three tests modes. These modes of operation are programmed by using the field CHMODE
(Channel Mode) in the mode register DBGU_MR.
The Automatic Echo mode allows bit-by-bit retransmission. When a bit is received on the DRXD line, it is sent to the
DTXD line. The transmitter operates normally, but has no effect on the DTXD line.
The Local Loopback mode allows the transmitted characters to be received. DTXD and DRXD pins are not used and the
output of the transmitter is internally connected to the input of the receiver. The DRXD pin level has no effect and the
DTXD line is held high, as in idle state.
The Remote Loopback mode directly connects the DRXD pin to the DTXD line. The transmitter and the receiver are
disabled and have no effect. This mode allows a bit-by-bit retransmission.
1292
SAM9G25 [DATASHEET]
Atmel-11032E-ATARM-SAMG25-Datasheet_13-Oct-14