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.