atm8 prg

Posted on Feb 4, 2014

This project describes how to build a simple programmer for the Atmel ATmega8 single-chip microcontrollers. This should be considered a `hobby grade` programmer as it does not use a variable Vcc and uses the `Serial Programming Algorithm. ` The ATmega8 can be configured (through programmable fuses) to disable the Serial Programming mode. Once di

atm8 prg
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sabled, a parallel programmer is required to re-enable the serial programming fuse. The programmer hardware consists of a 28 pin socket for the ATmega8 and a 14 pin header for connecting to the SBC2`s onboard 65C22. Please note that this can be adapted for use with any 65C22. The ATmega8 uses 5 pins for serial programming (in addition to Vcc and Gnd): Port Pin Function Description J1 PIN PORT PB5 19 (sck) shift clock 5 11 PB1 PB4 18 (MISO) data output 3 12 PB2 PB3 17 (MOSI) data input 4 10 PB0 PC6 1 (/RES) /Reset 9 16 PB6 PB6 9 (CLK IN) External Clock 10 17 PB7 The Atmega8 requires a valid clock input during programming. If the fuses are set to use an external clock source, then one will need to be provided. I chose to use the 65C22 Timer 1 output through PB7 to supply the clock. This ensures a valid clock is always present. Therefore, we will use Port B of the 65C22 to access the Programmer. Programming the ATmega8 is done by placing the part into RESET and applying serial commands and data to the data in pin while clocking the sck pin. Data read back from the part is clocked in on the data out pin. There are commands to read and write program memory, EEPROM memory, and the configuration area (fuse bytes, lock bits, signature bytes, and calibration bytes). Since the AVR Development tools create an Intel-Hex formatted output file, I decided to incorporate a modified version of Ross Archer`s "Intel Hex Downloader" which...

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