Atmel ATSTK500 500 Starter kit and development system. ATSTK500 ATSTK500 데이터 시트

1925C–AVR–3/03

Figure 3-2.  Implementation of LEDs and LED Headers

The AVR can source or sink enough current to drive a LED directly. In the 
STK500 design, a transistor with two resistors is used to give the same amount 
of light from the LED, whatever the target voltage (VTG) may be and to turn off 
the LEDs when VTG is missing.

The switches connected to the debug headers are implemented as shown in Figure 3-3.

Pushing a switch causes the corresponding SWx to be pulled low, while releasing it will
result in VTG on the appropriate switch header connector. Valid target voltage range is
1.8V < VTG < 6.0V.

Figure 3-3.  Implementation of Switches and Switch Headers

In the AVR, the user can enable internal pull-ups on the input pins, removing the 
need for an external pull-up on the push-button. In the STK500 design, we have 
added an external 10K pull-up to give all users a logical “1” on SWn when the 
push-button is not pressed. The 150R resistor limits the current going into the 
AVR.

LED1
LED3
LED5
LED7
VTG

LED0
LED2
LED4
LED6

GND

1   2

LEDn

10K

VTG

+5V

150R

10K

150R

VTG

SWn

SWn

SW1
SW3
SW5
SW7
VTG

SW0
SW2
SW4
SW6

GND

1   2