Introduction

In-System Programming allows programming and reprogramming of any AVR microcontroller positioned inside the end system. Using a simple Three-wire SPI interface, the In-System Programmer communicates serially with the AVR microcontroller, reprogramming all non-volatile memories on the chip.

In-System Programming eliminates the physical removal of chips from the system. This will save time, and money, both during development in the lab, and when updating the software or parameters in the field.

This application note shows how to design the system to support In-System Programming. It also shows how a low-cost In-System Programmer can be made, that will allow the target AVR microcontroller to be programmed from any PC equipped with a regular 9-pin serial port. Alternatively, the entire In-System Programmer can be built into the system allowing it to reprogram itself.