ATMEGA640 datasheet(301/436 Pages) MICROCHIP

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ATmega640/V-1280/V-1281/V-2560/V-2561/V [DATASHEET]

DS40002211A

28.6 Boundary-scan Related Register in I/O Memory

28.6.1

MCUCR – MCU Control Register

The MCU Control Register contains control bits for general MCU functions.

• Bits 7 – JTD: JTAG Interface Disable

When this bit is zero, the JTAG interface is enabled if the JTAGEN Fuse is programmed. If this bit is one, the JTAG

interface is disabled. In order to avoid unintentional disabling or enabling of the JTAG interface, a timed sequence

must be followed when changing this bit: The application software must write this bit to the desired value twice

within four cycles to change its value. Note that this bit must not be altered when using the On-chip Debug system.

28.6.2

MCUSR – MCU Status Register

The MCU Status Register provides information on which reset source caused an MCU reset.

• Bit 4 – JTRF: JTAG Reset Flag

This bit is set if a reset is being caused by a logic one in the JTAG Reset Register selected by the JTAG instruction

AVR_RESET. This bit is reset by a Power-on Reset, or by writing a logic zero to the flag.

28.7 ATmega640/1280/1281/2560/2561 Boundary-scan Order

Table 28-1 on page 302 shows the Scan order between TDI and TDO when the Boundary-scan chain is selected

as data path. Bit 0 is the LSB; the first bit scanned in, and the first bit scanned out. The scan order follows the pin-

out order as far as possible. Therefore, the bits of Port A and Port K is scanned in the opposite bit order of the other

ports. Exceptions from the rules are the Scan chains for the analog circuits, which constitute the most significant

bits of the scan chain regardless of which physical pin they are connected to. In Figure 28-3 on page 299, PXn.

Data corresponds to FF0, PXn. Control corresponds to FF1, PXn. Bit 4, bit 5, bit 6 and bit 7 of Port F is not in the

scan chain, since these pins constitute the TAP pins when the JTAG is enabled.

28.8 Boundary-scan Description Language Files

Boundary-scan Description Language (BSDL) files describe Boundary-scan capable devices in a standard format

used by automated test-generation software. The order and function of bits in the Boundary-scan Data Register

are included in this description. BSDL files are available for ATmega1281/2561 and ATmega640/1280/2560.

Bit

543

0x35 (0x55)

JTD

–

PUD

–

IVSEL

IVCE

MCUCR

Read/Write

R/W

Initial Value

Bit

543

0x34 (0x54)

–

–JTRF

WDRF

BORF

EXTRF

PORF

MCUSR

Read/Write

R/W

Initial Value

See Bit Description

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