SAM7S256_14 Datasheet, PDF (222/775 Pages) ATMEL Corporation – ARM-based Flash MCU

Figure 26-11. Test Modes
Automatic Echo
Receiver
RXD
Transmitter
Disabled
TXD
Local Loopback
Receiver
Transmitter
Disabled _RXD
VDD
Disabled _TXD
Remote Loopback
Receiver
V_DD
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 gener-
ate 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:
SAM7S Series [DATASHEET]
6175M–ATARM–26-Oct-12
222