269
8272E–AVR–04/2013
ATmega164A/PA/324A/PA/644A/PA/1284/P
The JTAG programming capability supports:
Flash programming and verifying
EEPROM programming and verifying
Fuse programming and verifying
Lock bit programming and verifying
The Lock bit security is exactly as in parallel programming mode. If the Lock bits LB1 or LB2 are
programmed, the OCDEN Fuse cannot be programmed unless first doing a chip erase. This is a
security feature that ensures no back-door exists for reading out the content of a secured
device.
The details on programming through the JTAG interface and programming specific JTAG
24.9
Bibliography
For more information about general Boundary-scan, the following literature can be consulted:
IEEE: IEEE Std. 1149.1-1990. IEEE Standard Test Access Port and Boundary-scan
Architecture, IEEE, 1993
Colin Maunder: The Board Designers Guide to Testable Logic Circuits, Addison-Wesley, 1992
24.10 Register description
24.10.1
OCDR – On-chip Debug Register
The OCDR Register provides a communication channel from the running program in the micro-
controller to the debugger. The CPU can transfer a byte to the debugger by writing to this
location. At the same time, an internal flag; I/O Debug Register Dirty – IDRD – is set to indicate
to the debugger that the register has been written. When the CPU reads the OCDR Register the
seven LSB will be from the OCDR Register, while the MSB is the IDRD bit. The debugger clears
the IDRD bit when it has read the information.
In some AVR devices, this register is shared with a standard I/O location. In this case, the OCDR
Register can only be accessed if the OCDEN Fuse is programmed, and the debugger enables
access to the OCDR Register. In all other cases, the standard I/O location is accessed.
Refer to the debugger documentation for further information on how to use this register.
Bit
7
65
43
21
0
MSB/IDRD
LSB
OCDR
Read/Write
R/W
Initial Value
0