Using external voltage reference
When the AREF0/AREF1 jumper is disconnected, ADC reference voltage can be supplied from an external source, by
connecting to the AREF0/AREF pins on the AUX header.
When using external an source for AREF, the user must control that VTARGET is at a higher voltage level than AREF. This
can be controlled easily by reading the VTG value from AVR Studio before setting AREF.
NOTE: The AREF0 and AREF1 voltage which are visible in the PC software are the STK600 generated voltages. Externally applied AREF voltages
cannot be read from AVRStudio.
Using the internal voltage reference
If the AVR's internal voltage reference is used, the AREF0/AREF1 jumper must be removed.
Using Aref as analog input
AREF0 and AREF1 can also be used as analog inputs to any of the ADC channels.
For tiny and mega devices, where only AREF0 is connected to the device via the routing card, AREF1 can be connected to a ADC channel by
connecting a cable from AREF1 on the AUX header and to the port pin header corresponding to the adc channel. (check the device datasheet for
which port pin header to connect to).
If the AVR's internal voltage reference, or an external voltage reference is used, the AREF0/AREF1 jumper must be removed. If this is the case,
AREF0 or AREF1 can be used as analog inputs by connecting a cable from pin 1 on the AREF0/AREF1 header to the port pin header corresponding
to the adc channel.
AREF decoupling capacitor
The routing card has a decoupling capacitor on AREF. This is marked with silkprint on the PCB. For some AVR devices the AREF pin is on a pin
which also is part of the high-voltage programming interface. On these routing cards the aref capacitor is not mounted, as it would make it
impossible to use the high-voltage programming interface. A capacitor can be soldered to achieve better noise performance. A typical value is 10nF.
The footprint for the capacitor is SMD size 0603.
Short circuit protection
The internal AREF voltage generators have a short circuit protection. If the STK600 measures the AREF0/AREF1 to be 0.3V or more below the
setpoint, AREF will be shut off. When this happens, the status LED will blink red. The AREF0 and AREF1 will also be shut down by the Master
MCU if a short circuit is detected on VTarget (in addition to shutting down VTarget). In this case, the status LED will blink red.
RESET Control
The STK600 controls the RESET signal to the target AVR. Under normal operation, the RESET line is held in an inactive, high state (pull-up to
VTG).
The RESET jumper
The RESET jumper connects the RESET pin on the target AVR to the STK600. When the RESET jumper is
mounted, STK600 controls the RESET signal. When the RESET jumper is not mounted, the RESET signal is
disconnected. This latter is useful for prototyping applications with an external reset system.
The RESET jumper must always be mounted when High-Voltage programming an AVR device. If using an external
reset system, it must allow the reset line to be controlled by the STK600 during programming.
The RESET button
STK600 has a reset button that resets the target AVR when being pushed. The button has no function if the RESET jumper is not mounted.
RESET signal on AUX header
The target AVR's RESET signal is accessible on the AUX header. This pin can be used to apply an external RESET signal. When applying an
external reset signal, the reset jumper must be removed.
12V Programming Voltage
During High-Voltage Programming, STK600 applies 12V to the AVR’s RESET line. Thus, an external reset circuit not capable of handling this
must be disconnected before High-Voltage programming the AVR.
External RESET de-coupling
When connected to an external system, there is often an external pull-up resistor and a capacitor connected to the reset line. A typical reset
connection is shown below.
Page 12 of 35
STK600 User Guide
2008-06-20
file://C:\Documents and Settings\PAWEL\Ustawienia lokalne\Temp\~hhE369.htm
