Datasheet

 2017 Microchip Technology Inc. DS60001516A-page 329
SAM9G20
Figure 27-11: Transmitter Control
27.4.4 Peripheral Data Controller
Both the receiver and the transmitter of the Debug Unit's UART are generally connected to a Peripheral Data Controller (PDC) channel.
The peripheral data controller channels are programmed via registers that are mapped within the Debug Unit user interface from the offset
0x100. The status bits are reported in the Debug Unit status register DBGU_SR and can generate an interrupt.
The RXRDY bit triggers the PDC channel data transfer of the receiver. This results in a read of the data in DBGU_RHR. The TXRDY bit
triggers the PDC channel data transfer of the transmitter. This results in a write of a data in DBGU_THR.
27.4.5 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 trans-
mitter 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.
DBGU_THR
Shift Register
DTXD
TXRDY
TXEMPTY
Data 0Data 1
Data 0
Data 0
Data 1
Data 1S
S PP
Write Data 0
in DBGU_THR
Write Data 1
in DBGU_THR
stop
stop