LPCXpresso IDE中的主题 Re: micro sd card pullups

micro sd card pullups

lpcware — Thu, 16 Jun 2016 02:55:38 GMT

Content originally posted in LPCWare by curtvm on Wed Feb 16 04:54:35 MST 2011
I created a little dip adapter board-
http://www.mtcnet.net/~henryvm/lpc1a.jpg
where the main goal was to be able to use a lpc11/13 on a breadboard, without having to buy an xpresso board for each 'project'. It works fine, but the micro sd socket I added (since I had the room anyway) don't have any pullups and I left the dat1/2 pins unconnected since spi mode was to be used.

The problem I have seems to be that leaving the dat1/2 pins floating is causing the initialization to fail at ACMD41(I am using an appnote for the lpc1700, which I modified for my lpc1114). If I probe those 2 dat pins with a pullup to 3.3v, then everything works fine. I have tried 3 different sd cards (2gb/4gb), but they are all sandisk cards. Maybe I need to try another brand to see if its any different.

Is there some definitive answer about these unused dat pins, whether pullups are required or not? In the case of the cards I have, it seems to be the case, but I have seen various schematics that leave these pins unconnected, such as http://elm-chan.org/works/sd20p/sdsg.png (I would think he would know). Is there anyone else that has a working board or adapter that leaves these pins floating?

Thanks.

Re: micro sd card pullups

lpcware — Thu, 16 Jun 2016 02:55:39 GMT

Content originally posted in LPCWare by Ex-Zero on Wed Feb 16 06:14:59 MST 2011
MicroSD P1 and P8 are not used in SPI mode (and therefore not connected) :)

See:

http://www.robotshop.com/PDF/microSD_Spec.pdf

A working SPI 1768 connection is:

P1 - nc
P2 - CS -> SSEL
P3 - DI -> MOSI
P4 - VDD -> 3.3V
P5 - SCLK-> SCK
P6 - VSS -> GND
P7 - DO -> MISO
P8 - nc

Re: micro sd card pullups

lpcware — Thu, 16 Jun 2016 02:55:40 GMT

Content originally posted in LPCWare by jharwood on Wed Feb 16 10:16:27 MST 2011
I can confirm that too. Dat1/2 not connected, 1gB Sandisk microSD on an LPC1343.

Re: micro sd card pullups

lpcware — Thu, 16 Jun 2016 02:55:41 GMT

Content originally posted in LPCWare by curtvm on Wed Feb 16 12:10:33 MST 2011
I'm just going to have to try a different brand sd card, and maybe make it a smaller one to boot, just to see what happens.

I'm not sure what is going on, but without the pullups on dat1/2 there is no response from ACMD41 (first 2 commands in initialization- CMD0 and CMD8, work ok). It just doesn't make sense, as the previous commands work, and by the time I get to where it fails, it is already in spi mode,

About the only info I can find, is the recommendation that these unused pins should not be left floating to prevent excess current draw. I guess from now on, I pull these up no matter what.

Re: micro sd card pullups

lpcware — Thu, 16 Jun 2016 02:55:41 GMT

Content originally posted in LPCWare by curtvm on Thu Feb 17 05:55:39 MST 2011
I'll also ask another question here since I am thinking about this-

As an alternative to sd cards, is it possible to use a usb flash drive as local storage from something like a lpc1343, or is it not possible to do a host function unless you have something like a lpc17xx? I really don't know what details are involved with getting a usb host working for a mass storage device, but I assume it would be similar to the sd card, where the file system stuff basically just needs an interface to/from the usb flash drive. I think I have seen the avr usb demos (LUFA) which include some host type stuff (where I think the avr used only has device support). Not quite sure, though.

The sd cards are nice because they are pretty simple (relatively speaking), but I would prefer not having to deal with sd card readers, micro adapters, etc. There are also some usb flash drives out there which are pretty small (flat, with exposed connections).

Just wondering if there are better options if I make a version 2 of my little adapter board.

Re: micro sd card pullups

lpcware — Thu, 16 Jun 2016 02:55:42 GMT

Content originally posted in LPCWare by igorsk on Thu Feb 17 07:00:39 MST 2011
LPC1768/1769 does have a USB Host function. See USBHostLite on NXP's site.