I want to utilize MMC2 slot and have already read this article: http://tiexpressdsp.com/index.php/SD-MMC_Usage_Notes_on_OMAP35x
TI guys recommend some level shifter in BGA package which is not appropriate for my application. Is there a possibility to use any of usual TSOP shifters and which? I saw some on the Zippy board but don’t a schematic for it.
Many thanks in advance!
Do you mean some voltage transfer chip ie : TXS0104 ?
2010/4/9 Maxim Podbereznyy <email@example.com>
Well, it depends. Are you lookng for 4 bit or 8 bit? There are some control leads that will switch the directions for a 4 bit, but 8 bit needs to be auto sensing and that can be an issue because the autosensing devices are not fast enough in there direction switching to support the speeds needed…
I am using the SN74LVC8T245 (which is currently quite hard to get) for
my single direction 1V8 to 3V3 8-bit buffering. For the 3V3 to 1V8
direction I use simple resistor dividers. If you want bi-directional
8-bit buffering, Analog Devices has a nice (but relatively expensive)
chip, the ADG3308. Probably there are several others as well...
Hope this helps,
Not really. Please look at TI SN74LVC8T245 and Analog Devices ADG3308.
Can they do what you want?
Thank you very much for all these answers!
I can see ADG3308 is very simple to integrate as it is on stock in local store. I just don’t understand the thing with all those direction signals on MMC2. Can’t I just set DAT0…DAT3 lines as MMC_DAT0…MMC_DAT3 and use bidirectional voltage shifter like ADG3308?
David thank you for the Zippy schematic! I can only order 74AVC4T774 with 4wk lead time. It is not very good…
P.S. also did not know about Micrel SPI controller, very good information! Again thank you!
2010/4/9 David Anders <firstname.lastname@example.org>
generally speaking generic bi-directional level shifters don’t work well with SD/MMC due to some of the timming features of the protocol. there are a wide range of variations of the 74AVC4T774 that could be used and a number of parts suppliers like Mouser, Avnet, and Digikey have them in stock.
in order use general level sifters such as the 74AVC4T774, as opposed to ASIC level shifters like the TXS0206, you need to have control lines to determine direction of the signal. the OMAP3 sd/mmc interface has a mode to support this configuration.