AVR910 In-System Programming

　　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.