ATMEGA32A_14 Datasheet, PDF (218/336 Pages) ATMEL Corporation – 8-bit Microcontroller with 32KBytes In-System Programmable Flash

Figure 25-2. Reset Register
From other Internal and
External Reset Sources
From
TDI
To
TDO
DQ
Internal Reset
ClockDR · AVR_RESET
25.3.4 Boundary-scan Chain
The Boundary-scan Chain has the capability of driving and observing the logic levels on the digital I/O pins, as well
as the boundary between digital and analog logic for analog circuitry having Off-chip connections.
See “Boundary-scan Chain” on page 236 for a complete description.
25.4
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-impedance 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.
25.4.1 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 contents 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.
25.4.2 IDCODE; $1
Optional JTAG instruction selecting the 32-bit ID-register as Data Register. The ID-register consists 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.
ATmega32A [DATASHEET]
Atmel-8155D-AVR-ATmega32A-Datasheet_02/2014
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