ATmega161 datasheet(28/61 Pages) ATMEL

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Hardware Description

3-18

AVR STK500 User Guide

1925C–AVR–3/03

Figure 3-24. Internal AREF Connection

The AVR Studio-controlled analog reference voltage can also be used as an input to the

analog comparator or for ADC measurements on the AVR. AVR’s AREF signal can then

be connected to VTG.

The internal AREF has a short circuit protection. If an AREF value is set up to be higher

than 0.3V and the master microcontroller measures it to be below 0.3V for a duration of

80 ms, the master microcontroller will shut off the AREF. When this happens, the status

LED will blink slowly.

The AREF will also be shut down by the master microcontroller if a short circuit is

detected on VTARGET (in addition to shutting down VTARGET). In this case, the status

LED will blink quickly.

3.8.3

Reset Settings,

RESET

The RESET jumper controls the RESET signal to the STK500. When ISP programming

the target device in the socket, the master microcontroller programs the AVR device

without interfering with the application. When the RESET jumper is mounted, the master

microcontroller controls the RESET signal of the AVR. When the RESET jumper is not

mounted, the RESET signal is disconnected. This is useful for prototype applications

with an external reset system.

The RESET jumper must always be mounted when High-voltage Programming an AVR

device. When using an external reset system, it must allow the reset line to be controlled

by the master microcontroller reset system during programming. The RESET button is

disconnected if the RESET jumper is not mounted. Figure 3-25 explains the RESET

jumper options.

PE1

RST

GND

XT2

VTG

PE0

PE2

REF

XT1

GND

1 2

Master

MCU

AREF

PWM

AREF

PORTE/AUX

Jumper

Voltage

regulator

10 - 15V

VIN

0 - 6V

ADC

ATmega161 Datasheet(PDF) 28 Page - ATMEL Corporation

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