Datasheet

Table Of Contents
225
2570N–AVR–05/11
ATmega325/3250/645/6450
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
25.3.2.1 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.
25.3.2.2 Part Number
The part number is a 16-bit code identifying the component. The JTAG Part Number for Atmel
ATmega325/3250/645/6450 is listed in Table 25-1.
25.3.2.3 Manufacturer ID
The Manufacturer ID is a 11-bit code identifying the manufacturer. The JTAG manufacturer ID
for ATMEL is listed in Table 25-2.
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 “Clock
MSB
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
Table 25-1. AVR JTAG Part Number
Part Number JTAG Part Number (Hex)
ATmega325 0x9505
ATmega3250 0x9506
ATmega645 0x9605
ATmega6450 0x9606
Table 25-2. Manufacturer ID
Manufacturer JTAG Manufacturer ID (Hex)
ATM E L 0x 0 1F