I'm putting this out because I know there are some who tinker with microcontroller applications on the list. I can't really get an answer from web searches. At any rate, I've got an ATMega AVR that I'm using with SDCards in SPI mode. I've got a random assortment of MMC and SD and SDHC cards and they all seem to work as expected--until I ran into a bunch of Kingston 4GB Class 4 SDHC cards (model SD-K04G). Then things fall apart. The cards function normally in SD mode. SanDisk 4GB SDHC cards work just fine. Here's the SPI conversation from its start: Sending: 40 00 00 00 00 95 Receiving: 01 Sending: 48 00 00 01 AA 87 Receiving: 05 Sending: 41 00 00 00 00 01 Receiving: 05 Note that both CMD8 and CMD1 fail with "illegal operation". I'm running the SPI clock at about 250KHz, so speed isn't the issue. Can anyone shed any light on this? --Chuck