Datasheet

ATmega164A/PA/324A/PA/644A/PA/1284/P
 2018 Microchip Technology Inc. Data Sheet Complete DS40002070A-page 267
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 microcontroller 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 6543210
0x31 (0x51) 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