Datasheet
246
ATmega169A/PA/329A/PA/649A/P/3290A/PA/6490A/P [DATASHEET]
8284E–AVR–02/2013
26.3 Data registers
The data registers relevant for Boundary-scan operations are:
• Bypass Register
• Device Identification Register
• Reset Register
• Boundary-scan Chain
26.3.1 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 Regis-
ter can be used to shorten the scan chain on a system when the other devices are to be tested.
26.3.2 Device Identification Register
Table 26-1 shows the structure of the Device Identification Register.
Table 26-1. The Format of the Device Identification Register
26.3.2.1 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.
26.3.2.2 Part Number
The part number is a 16-bit code identifying the component. The JTAG Part Number is listed in Table 28-6 on page
296.
26.3.2.3 Manufacturer ID
The manufacturer ID is a 11-bit code identifying the manufacturer. The JTAG manufacturer ID for Atmel is listed in
Table 28-6 on page 296.
26.3.3 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 settings for the clock options, the part will
remain reset for a reset time-out period (refer to ”Clock sources” on page 30) after releasing the Reset Register.
The output from this Data Register is not latched, so the reset will take place immediately, as shown in Figure 26-1.
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