I'm working on a custom-designed board (designed by someone from this forum) with some rather odd results. I wonder if anyone can give some clues.
The processor is an Atmega2560, and it is connected to a USB port via a FT232RLSSOP FTDI chip. The processor is running (or appears to be) at 16 MHz from a nearby crystal.
What I can do ...
- I can "talk" to the Atmega2560 chip using ICSP interfacing.
- I've uploaded a bootloader.
- I can upload a sketch using this bootloader on my Windows XP PC.
What I can't do ...
- I can't upload sketches using the bootloader (same USB cable) from my Mac, although the same Mac is what I normally use to upload to Unos, Mega 2560 boards, Leonardo etc.
- If I upload a "communications" sketch like the "ASCIITable" that comes with the IDE, nothing appears in the serial monitor, or occasionally just a line or two.
- Different baud rates don't help, either I see nothing or just a few characters.
- Adding a delay in the loop of ASCIITable seems to make things worse, nothing appears at all.
I don't understand how the USB serial interface can work to upload a sketch, using the bootloader, at 115200 baud, but if the sketch itself writes out data at 115200 baud, that data doesn't appear.
All of the chips are SMD devices, and it is difficult or impossible to connect up the logic analyzer to see what signals, if any, are travelling between the main processor and the FT232 chip.
The client for whom the board is being developed, on the other hand, was able to upload the ASCIITable sketch, and have it work perfectly. That appears to rule out egregious errors, like a missing link or solder bridge on the board. Plus, the fact that sketches can be uploaded using the bootloader also appears to rule out major design or implementation errors.
Any suggestions welcome.