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Questions relating to designing PCBs
By jhaislip
#175654
Hi all,

If I have an Atmega1280 connected to a MAX3421 USB Host Controller via SPI, am I going to have problems when I try to program the Atmega via the AVRISP mkII? I'm having a hard time seeing how the AVRISP mkII is able to 'select' the Atmega. The programmer connects to the standard SCK, MOSI, MISO, RESET, +5V, and GND on the Atmega, but the MAX3421 also connects to MOSI, MISO, and SCK.

Thanks for helping me understand this.

-Josh
By jhaislip
#175657
I am connecting the SS pin on the 3421 to a DIO pin on the Atmega via a level shifter. My concern was whether at DIO pin would be high, low, or floating during programming via the AVRISP mkII. Do I have any control over this during programming without additional circuitry?

EDIT: I forgot to mention the level shifter.
By jremington
#175681
After a reset, all port pins on an ATmega are inputs, and floating. They should not do anything else during programming, but I've never checked. This is probably a question for the AVRFreaks forum, but I'll bet that a pullup resistor on /SS will prevent the 3421 from seeing anything on the bus, until it is properly pulled down.