ATmega165 datasheet(216/336 Pages) ATMEL

216 / 336 page

216

ATmega165/V

2573G–AVR–07/09

MCU Status Register –

MCUSR

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.

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 connection.

Scanning the Digital Port Pins

Figure 101 shows the Boundary-scan Cell for a bi-directional port pin with pull-up func-

tion. The cell consists of a standard Boundary-scan cell for the Pull-up Enable – PUExn

– function, and a bi-directional pin cell that combines the three signals Output Control –

OCxn, Output Data – ODxn, and Input Data – IDxn, into only a two-stage Shift Register.

The port and pin indexes are not used in the following description

The Boundary-scan logic is not included in the figures in the datasheet. Figure 102

shows a simple digital port pin as described in the section “External Interrupts” on page

51. The Boundary-scan details from Figure 101 replaces the dashed box in Figure 102.

When no alternate port function is present, the Input Data – ID – corresponds to the

PINxn Register value (but ID has no synchronizer), Output Data corresponds to the

PORT Register, Output Control corresponds to the Data Direction – DD Register, and

the Pull-up Enable – PUExn – corresponds to logic expression PUD · DDxn · PORTxn.

Digital alternate port functions are connected outside the dotted box in Figure 102 to

make the scan chain read the actual pin value. For Analog function, there is a direct

connection from the external pin to the analog circuit, and a scan chain is inserted on

the interface between the digital logic and the analog circuitry.

Bit

765

432

–

–JTRF

WDRF

BORF

EXTRF

PORF

MCUSR

Read/Write

R/W

Initial Value

See Bit Description

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