3 Programming Protocol

Immediately after Reset goes active on the target AVR microcontroller, the chip is ready to enter Programming mode. The internal Serial Peripheral Interface (SPI) is activated, and is ready to accept instructions from the programmer. On the AT90S1200, it is very important to keep the SCK pin stable, as one single edge will cause the target to lose synchronization with the programmer. For other devices, use the synchronization algorithm specified in the datasheet. After pulling Reset low, wait at least 20ms before issuing the first command.