dual SD cards

jeremywilson · Joined: 11 Jul 2011 Posts: 79 Location: United States

I currently use AVR-DOS with single SD card circuits with no problems. However, I need to add a second SD card. With AVR-DOS, I can only define one chip select (CS) pin.
Is there a way to add a second CS (I don't do assembly language) with AVR-DOS?
Would it be better or easier to just use an MCU pin to power the SD cards, then turn on the one I need to write to? (bad thing to frequently power SD card on/off?)
I could add glue logic ICs to route the CS signal, but prefer not to.

Paulvk · Joined: 28 Jul 2006 Posts: 1257 Location: SYDNEY

I used a multiplexer to run two LCDs off one micro
you could do similar with logic gates and another
cpu pin to chose which sd card the CS activates
Regards Paul

jeremywilson · Joined: 11 Jul 2011 Posts: 79 Location: United States

I may have to use a multiplexer or switch. Or MCU-controlled mosfets to power the cards.
I think there will be other issues with AVR-DOS, though, such as, reading data from one card and writing to the other card. Probably would have to read some data and store in MCU RAM, initialize other card, then write data to it, then re-init first SD, etc...

Paulvk · Joined: 28 Jul 2006 Posts: 1257 Location: SYDNEY

The mega1284 is good for a task like that with its 16K of ram and 20mhz
you can make large buffers.
I have to re initialize the LCDs as well
Regards Paul