Hardware Description
3-16 AVR STK500 User Guide
1925C–AVR–3/03
3.8.1 Target V
CC
Settings,
VTARGET
VTARGET controls the supply voltage to the target AVR microcontroller sockets. It can
either be controlled from AVR Studio or supplied from an external source. If the VTAR-
GET jumper is mounted, the on-board supply voltage is connected. The on-board
supply voltage can be adjusted to 0 - 6V from AVR Studio. Always verify the respective
datasheet for the AVR device operating voltage before adjusting VTARGET voltage.
Using the on-board supply voltage, approximately 0.5A can be delivered to the target
section. See “Appendix A” in Section 10.
If the VTARGET jumper is disconnected, target V
CC
must be supplied from an external
source at one of the VTG pins on the PORT headers. Figure 3-21 explains VTARGET
jumper options.
When using an external source for VTARGET, the user must control that VTARGET is
at a higher voltage level than AREF (analog reference voltage). Always connect com-
mon ground (GND) when using an external VTARGET voltage.
Figure 3-21. VTARGET Jumper Options
The STK500 master microcontroller controls the target voltage using the internal PWM.
Figure 3-22 shows the internal connection of the VTARGET signal.
Figure 3-22. VTARGET Connection
Note: The green LED will light when there is a voltage available on the VTG NET. It’s
impossible to use the debug or programming area of STK500 without VTG.
VTARGET
AREF
VTARGET
AREF
Jumper Mounted
Jumper not Mounted
On-board VTARGET supply connected (default)
On-board VTARGET supply disconnected
Master
MCU
VTARGET
PWM
VTG NET
Green LED
Jumper
Voltage
Regulator
10 - 15V
VIN
0 - 6V
Wr
Rd
ADC
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