I have an Arduino Pro Mini, 3v3, 8Mhz. I have in the past successfully programmed it over the serial line. I have two others, I can program them over the serial line. I can program the first one using SPI. Once programmed, I can communicate both ways over its serial lines. So I'm certain that the serial port is good, the board is good, and my connections are good.

I suspect it may be a corrupt bootloader. I have burned the bootloader using IDE. It still does the same thing.

What else could it be?

  • If you program the chip using ISP you will overwrite the boot loader. – Gerben Jan 21 '17 at 12:07
  • I don't think we're talking about the same thing. I'm talking about SPI, not ISP. Using the MOSI, MISO, and CLK pins, instead of RX and TX. – RichieACC Jan 21 '17 at 13:11
  • ISP is In-System Programming. The protocol looks a lot like SPI and it uses the same pins. So we are talking about the same thing. – Gerben Jan 21 '17 at 13:16
  • Ok. So then in theory, if I burn the bootloader, then the serial programmer should work again? But as I said, it didn't work. Unless the bootloader that I used wasn't the right one. – RichieACC Jan 21 '17 at 13:58

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