In System Programming (ISP) for ATMEL chips


Posted on Feb 5, 2014

ISP is a way to serially program your microcontroller, while it resides in its place, in other words, without removing the chip from your board. Whether you`re just starting in the ATMEL microcontrollers, or you`re familiar with it, ISP (In System Programming) will provide you a simple and affordable home made solution to program and debug your microcontroller based project.


In System Programming (ISP) for ATMEL chips
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Sometimes, ISP can become very useful, when adjusting some delays, frequencies or any other values that you would intend to find by trial and error. a process that would otherwise take too much time. Normally, the flash memory of an ATMEL microcontroller is programmed using a parallel interface, which consists of sending the data byte by byte (using eight independent lines for the data, and another bunch of lines for the address, the control word and clock input). On the other hand ISP is performed using only four lines, and literally, data is transferred through two lines only, as in a I2C interface, where data is shifted in bit by bit though. MOSI(data input) line, with a clock cycle between each bit and the next (on the SCK(clock input) line). MISO (data output)line is used for reading and for code verification, it is only used to output the code from the FLASH memory of the microcontroller. The RST(used to activate the serial Programming) pin, which is normally used to reset the device, is also used to enable the three pins (MOSI, MISO and SCK) to be used for ISP simply by setting RST to HIGH (5V), otherwise if RST is low (0V), your program start running and those three pins, are used normally as P1. 5, P1. 6 and P1. 7. The Code memory array can be programmed using the serial ISP interface while RST is pulled to VCC. The serial interface consists of pins SCK, MOSI (input) and MISO (output). After RST is set high, the...




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