#avr Logs

Nov 27 2020

04:50 PM kdehl: I want to interface an AVR microcontroller (ATmega6450) to an SD card and to keep it simple, I'd figure I'd use SPI mode.
04:57 PM kdehl: If I connect it directly to the physical SPI bus on the controller, won't it conflict with the ISP?
04:58 PM LeoNerd: With AVR chips, it's usual to add some weak pullup resistors on the CS# lines to SPI slaves, so they all get deasserted (rather than float) when the chip is in reset mode for programming
04:59 PM LeoNerd: That should avoid the risk of the SD card accidentally trying to drive MISO
04:59 PM LeoNerd: Specifically in the case of SD cards, not overkill at all. I've known some SD cards to overheat and blow up (at least, metaphorically) when driving 5V IO into them
05:00 PM kdehl: Ah, good to know.
05:00 PM kdehl: Right, the pull-up is clever.
05:01 PM kdehl: Thanks fo the help! :)