271
8272E–AVR–04/2013
ATmega164A/PA/324A/PA/644A/PA/1284/P
25.3
Data Registers
The Data Registers relevant for Boundary-scan operations are:
Bypass Register
Device Identification Register
Reset Register
Boundary-scan Chain
25.3.1
Bypass Register
The Bypass Register consists of a single Shift Register stage. When the Bypass Register is
selected as path between TDI and TDO, the register is reset to 0 when leaving the Capture-DR
controller state. The Bypass Register can be used to shorten the scan chain on a system when
the other devices are to be tested.
25.3.2
Device Identification Register
Figure 25-1 shows the structure of the Device Identification Register.
Figure 25-1. The format of the device identification register.
Version
Version is a 4-bit number identifying the revision of the component. The JTAG version number
follows the revision of the device. Revision A is 0x0, revision B is 0x1 and so on.
Part Number
The part number is a 16-bit code identifying the component. The JTAG Part Number for Atmel
Manufacturer ID
The Manufacturer ID is a 11-bit code identifying the manufacturer. The JTAG manufacturer ID
25.3.3
Reset Register
The Reset Register is a test Data Register used to reset the part. Since the AVR tri-states Port
Pins when reset, the Reset Register can also replace the function of the unimplemented optional
JTAG instruction HIGHZ.
A high value in the Reset Register corresponds to pulling the external Reset low. The part is
reset as long as there is a high value present in the Reset Register. Depending on the fuse set-
tings for the clock options, the part will remain reset for a reset time-out period (refer to
”ClockMSB
LSB
Bit
31
28
27
12
11
1
0
Device ID
Version
Part Number
Manufacturer ID
1
4 bits
16 bits
11 bits
1-bit