Last updated on March 4, 2009
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Today I learned a little lesson about programming AVRs†. After sorting that out I was able to properly use the SDrive NUXX‘s onboard programmer with no problem. After that I thought it should have been working, but the device wouldn’t work. Poking around I found the AVR running, but then found that the SD card slot was only getting about 1V, which is far below the 3.3V it requires.
This problem turned out to be caused by the LE33CZ 3.3V LDOs that I’d ordered from Digi-Key. As can be seen here, when fed 5V the LDOs were putting out just over 1V whose datasheets I had read wrong. I stupidly missed the “from bottom” note on the pinout section and been both fitting and testing the part backwards. (This is another thing to fix in the v1.1 / production run.)
For testing last night I worked around this by feeding the SD card 3.3V from a benchtop supply, everything worked great. The following morning I understood my mistake and fitted the parts properly, and now the benchtop supply is no longer needed. The 2GB SD card I’d picked up for cheap at Micro Center worked great, and I had no problems loading most of the .ATR images which I’d tried.
There’s still a couple problems with the PCB, but I’ll sort those out before the production order. Most notably there is the missing traces in the programmer, then I also screwed up the switch marking silkscreen for the front panel. Whoops!
At least it’s working. Yay!
† On PICs, which I am more familiar with, one just connects the programmer to the programming pins on the chip and the firmware gets loaded, regardless of the clock setting on the chip. Well, on AVRs it seems that unless one is doing high voltage parallel programming one needs a clock connected to the chip which matches the current clock setting. If this doesn’t exist, the microcontroller won’t respond. If you change the chip’s configuration to something other than the current onboard clock (or internal clock) then the chip will essentially become unresponsive. It was a bit confusing to me.