
227
2503Q–AVR–02/11
ATmega32(L)
Figure 115. Reset Register
Boundary-scan Chain
The Boundary-scan Chain has the capability of driving and observing the logic levels on the dig-
ital I/O pins, as well as the boundary between digital and analog logic for analog circuitry having
Off-chip connections.
Boundary-scan
Specific JTAG
Instructions
The instruction register is 4-bit wide, supporting up to 16 instructions. Listed below are the JTAG
instructions useful for Boundary-scan operation. Note that the optional HIGHZ instruction is not
implemented, but all outputs with tri-state capability can be set in high-impedant state by using
the AVR_RESET instruction, since the initial state for all port pins is tri-state.
As a definition in this datasheet, the LSB is shifted in and out first for all Shift Registers.
The OPCODE for each instruction is shown behind the instruction name in hex format. The text
describes which Data Register is selected as path between TDI and TDO for each instruction.
EXTEST; $0
Mandatory JTAG instruction for selecting the Boundary-scan Chain as Data Register for testing
circuitry external to the AVR package. For port-pins, Pull-up Disable, Output Control, Output
Data, and Input Data are all accessible in the scan chain. For Analog circuits having Off-chip
connections, the interface between the analog and the digital logic is in the scan chain. The con-
tents of the latched outputs of the Boundary-scan chain is driven out as soon as the JTAG IR-
register is loaded with the EXTEST instruction.
The active states are:
Capture-DR: Data on the external pins are sampled into the Boundary-scan Chain.
Shift-DR: The Internal Scan Chain is shifted by the TCK input.
Update-DR: Data from the scan chain is applied to output pins.
IDCODE; $1
Optional JTAG instruction selecting the 32-bit ID-register as Data Register. The ID-register con-
sists of a version number, a device number and the manufacturer code chosen by JEDEC. This
is the default instruction after power-up.
The active states are:
Capture-DR: Data in the IDCODE-register is sampled into the Boundary-scan Chain.
Shift-DR: The IDCODE scan chain is shifted by the TCK input.
SAMPLE_PRELOAD;
$2
Mandatory JTAG instruction for pre-loading the output latches and talking a snap-shot of the
input/output pins without affecting the system operation. However, the output latches are not
connected to the pins. The Boundary-scan Chain is selected as Data Register.
DQ
From
TDI
ClockDR AVR_RESET
To
TDO
From other Internal and
External Reset Sources
Internal Reset