SAM7X256_14 Datasheet, PDF (202/662 Pages) ATMEL Corporation – ARM-based Flash MCU

Figure 26-12. Test Modes
Automatic Echo
Receiver
RXD
Transmitter
Disabled
TXD
Local Loopback
Receiver
Transmitter
Disabled _RXD
V_DD
Disabled _TXD
Remote Loopback
Receiver
VDD
Disabled
RXD
Transmitter
Disabled
TXD
26.4.6 Debug Communication Channel Support
The Debug Unit handles the signals COMMRX and COMMTX that come from the Debug Communication Channel of the
ARM Processor and are driven by the In-circuit Emulator.
The Debug Communication Channel contains two registers that are accessible through the ICE Breaker on the JTAG
side and through the coprocessor 0 on the ARM Processor side.
As a reminder, the following instructions are used to read and write the Debug Communication Channel:
MRC
p14, 0, Rd, c1, c0, 0
Returns the debug communication data read register into Rd
MCR
p14, 0, Rd, c1, c0, 0
Writes the value in Rd to the debug communication data write register.
The bits COMMRX and COMMTX, which indicate, respectively, that the read register has been written by the debugger
but not yet read by the processor, and that the write register has been written by the processor and not yet read by the
debugger, are wired on the two highest bits of the status register DBGU_SR. These bits can generate an interrupt. This
feature permits handling under interrupt a debug link between a debug monitor running on the target system and a
debugger.
26.4.7 Chip Identifier
The Debug Unit features two chip identifier registers, DBGU_CIDR (Chip ID Register) and DBGU_EXID (Extension ID).
Both registers contain a hard-wired value that is read-only. The first register contains the following fields:
 EXT - shows the use of the extension identifier register
SAM7X Series [DATASHEET]
6120K–ATARM–11-Feb-14
202