Has anybody come across any issues downloading the bootloader from the Arduino Uno running on a 16MHz Clock to a slave Atmega 328 chip running on a 20MHz clock, will this affect the transmission speeds between devices? or do they both have to run on the same clock frequency. Anyone tried this?
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The difference in clock speed is not important. The programmer just has to use a data rate of 1/4 the target clock speed for clocks less than 12 MHz and 1/6th the clock speed for anything else. When the target is running at 20 MHz the clock pulses have to be LOW for at least 3 cycles and HIGH for at least 3 cycles. That gives a data rate up to 3.333 MHz. Any rate slower than that will work and since uploading to a factory default chip running at 1 MHz works, it is clear that the data rate is WAY under 3.333 MHz.