at91rm3400 ATMEL Corporation, at91rm3400 Datasheet - Page 187

• Manufacturer Part Number: at91rm3400
• Description: Atmel Advanced At91 Arm Microcontroller
• Manufacturer: ATMEL Corporation

Figure 63. Transmitter Control
Peripheral Data
Controller
Test Modes
1790A–ATARM–11/03
Shift Register
DBGU_THR
TXEMPTY
TXRDY
DTXD
in DBGU_THR
Write Data 0
S
Data 0
in DBGU_THR
Write Data 1
As soon as the first character is completed, the last character written in DBGU_THR is trans-
ferred into the shift register and TXRDY rises again, showing that the holding register is
empty.
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.
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 trans-
mitter. This results in a write of a data in DBGU_THR.
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 transmit-
ter and the receiver are disabled and have no effect. This mode allows a bit-by-bit
retransmission.
Data 0
Data 0
P
stop
S
Data 1
Data 1
P
AT91RM3400
Data 1
stop
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