Atmel AVR910 Application Note

AVR910: In-System Programming
Features
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Complete In-System Programming Solution for AVR Microcontrollers
•
Covers All AVR Microcontrollers with In-System Programming Support
•
Reprogram Both Data Flash and Parameter EEPROM Memories
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Complete Schematics for Low-cost In-System Programmer
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Simple Three-wire SPI Programming Interface
Introduction
In-System Programming allows programming and reprogramming of any AVR micro-
controller 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 updat-
ing the software or parameters in the field.
This application note shows how to design the system to support In-System Program-
ming. 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.
The Programming Interface
For In-System Programming, the programmer is connected to the target using as few
wires as possible. To program any AVR microcontroller in any target system, a simple
Six-wire interface is used to connect the programmer to the target PCB. Figure 1
below shows the connections needed.
The Serial Peripheral Interface (SPI) consists of three wires: Serial ClocK (SCK), Mas-
ter In – Slave Out (MISO) and Master Out – Slave In (MOSI). When programming the
AVR, the In-System Programmer always operate as the Master, and the target system
always operate as the Slave.
The In-System Programmer (Master) provides the clock for the communication on the
SCK Line. Each pulse on the SCK Line transfers one bit from the Programmer (Mas-
ter) to the Target (Slave) on the Master Out – Slave In (MOSI) line. Simultaneously,
each pulse on the SCK Line transfers one bit from the target (Slave) to the Program-
mer (Master) on the Master In – Slave Out (MISO) line.
8-bit
RISC
Microcontroller
Application
Note
Rev. 0943E–AVR–08/08