Rainbow Electronics ATmega128L - Manual (Page 242)

242
ATmega128(L)
2467B–09/01
• 2 single Program Memory break-points + 1 Data Memory break point with mask
“range break point”.
A debugger, like the AVR Studio ® , may however use one or more of these resources for
its internal purpose, leaving less flexibility to the end-user.
A list of the On-chip Debug specific JTAG instructions is given in “On-chip Debug Spe-
cific JTAG Instructions” on page 242.
The JTAGEN fuse must be programmed to enable the JTAG Test Access Port. In addi-
tion, the OCDEN fuse must be programmed and no lock bits must be set for the On-chip
debug system to work. As a security feature, the On-chip Debug system is disabled
when any lock bits are set. Otherwise, the On-chip Debug system would have provided
a back-door into a secured device.
The AVR Studio enables the user to fully control execution of programs on an AVR
device with On-chip Debug capability, AVR In-Circuit Emulator, or the built-in AVR
Instruction Set Simulator. AVR Studio supports source level execution of Assembly pro-
grams assembled with Atmel Corporation’s AVR Assembler and C programs compiled
with 3rd party vendors’ compilers.
AVR Studio runs under Microsoft ® Windows ® 95/98/2000 and Windows NT ® .
For a full description of the AVR Studio, please refer to the AVR Studio User Guide.
Only highlights are presented in this document.
All necessary execution commands are available in AVR Studio, both on source level
and on disassembly level. The user can execute the program, single step through the
code either by tracing into or stepping over functions, step out of functions, place the
cursor on a statement and execute until the statement is reached, stop the execution,
and reset the execution target. In addition, the user can have an unlimited number of
code breakpoints (using the BREAK instruction) and up to 2 data memory breakpoints,
alternatively combined as a mask (range) break-point.
On-chip Debug Specific
JTAG Instructions The On-chip debug support is considered being private JTAG instructions, and distrib-
uted within ATMEL and to selected third-party vendors only. Instruction opcodes are
listed for reference.
PRIVATE0; $8 Private JTAG instruction for accessing On-chip debug system.
PRIVATE1; $9 Private JTAG instruction for accessing On-chip debug system.
PRIVATE2; $A Private JTAG instruction for accessing On-chip debug system.
PRIVATE3; $B Private JTAG instruction for accessing On-chip debug system.
On-chip Debug Related
Register in I/O Memory
On-chip Debug Register –
OCDR
The OCDR register provides a communication channel from the running program in the
microcontroller to the debugger. The CPU can transfer a byte to the debugger by writing
Bit 7 6 5 4 3 2 1 0
MSB/IDRD LSB OCDR
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial value 0 0 0 0 0 0 0 0