Toggle CS for every SD command?

[mbro131]

Is it necessary to toggle the CS line before every command sent to an SD card? My interpretation of the specification is that it should be, however many of the examples given on this forum only seem to set CS high and then low prior to the software reset command (CMD0). I understand that this is a requirement in order to set the card in SPI mode.

Initially I thought that MMC (which is what most of the examples I have seen are for) did not require the card select toggle, but I implemented a system with a PIC18F2550 and SanDisk SD card and it doesn't seem to matter whether CS is toggled or not (except for prior to CMD0).

So if it works anyway, why do I ask? My system needs to be able to work with as many types/brands of SD cards as possible, just because the SanDisk card I am using works doesn't mean others will. I can't find anywhere in the specification how long the CS line should be held high for prior to a command.

Also, has anyone had a look at the legalities of posting code for interfacing with SD cards (I am assuming the SDA doesn't allow this?).

Matt

[Guest]

I would assume so, otherwise it would be hard/impossible to use multiple devices on the SPI bus. I toggle the CS line for every command in my projects.

[Guest]

Have you (or someone in your company) signed any NDA? If not, you can post it... IANAL, of course.