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To assure proper communication on the three SPI lines， it
is necessary to connect ground on the programmer to
ground on the target （GND）。
To enter and stay in Serial programming mode， the AVR
microcontroller reset line has to be kept active （low）。 Also，
to perform a Chip Erase， the Reset has to be pulsed to end
the Chip Erase cycle. To ease the programming task， it is
preferred to let the programmer take control of the target
microcontroller reset line to automate this process using a
fourth control line （Reset）。
To allow programming of targets running at any allowed
voltage （2.7V - 6.0V）， the programmer can draw power
from the target system （VCC）。 This eliminate the need for a
separate power supply for the programmer. Alternatively，
the target system can be supplied from the programmer at
programming time， eliminating the need to power the target
system through its regular power connector for the duration
of the programming cycle.
Figure 2 shows the connector used by this In-System programmer to connect to the target system. The standard
connector supplied is a 2 x 3 pin header contact， with pin
spacing of 100 mils.
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