Rainbow Electronics AT91CAP9S250A - Manual (Page 414)

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6264A–CAP–21-May-07
AT91CAP9S500A/AT91CAP9S250A
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 transmit-
ter. This results in a write of a data in DBGU_THR.
31.4.5 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 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.
Figure 31-12. Test Modes
31.4.6 Debug Communication Channel Support
The Debug Unit handles the signals COMMRX and COMMTX that come from the Debug Com-
munication Channel of the ARM Processor and are driven by the In-circuit Emulator.
Receiver
Transmitter
Disabled
RXD
TXD
Receiver
Transmitter
Disabled
RXD
TXD
V DD
Disabled
Receiver
Transmitter
Disabled
RXD
TXD
Disabled
Automatic Echo
Local Loopback
Remote Loopback V
DD