MMC SPI interfacing

[Wizard]

Hi there!

I'm adding a mmc card to my data adquisition project. I'm using a pic18f4550 with usb conection implemeted. I use a 1.8k and 3.3k voltage divider circuit to convert the 5V from the pic to aporx. 3V to the card. As in: http://www.cc5x.de/MMC/
I know that it doesn't suit the standart but peolple have it working. So far I have tried the mmc_spi.c drivers, without good results. I have tested it with two mmc cards(32mb and 256mb) I got nothing from the 256 one. With the 32mb card I can reset it with some problems:

[PCM programmer]

See this thread for already translated code:
http://www.ccsinfo.com/forum/viewtopic.php?t=23183&start=15

Also do a search of the forum for "MMC". There are many threads
on that circuit, and the problems that it has, such as level translators
and the lack of 100K pull-up resistors, etc. Read the link I posted
and read all the MMC threads before going any further.
http://www.ccsinfo.com/forum/search.php

[ckielstra]

[Guest]

Thanks ckielstra, that was my fault. Now, when the card its reseted I can write and read from the mmc card without problems. BUT the problem its to reset the card

I explain, when I power on th system and the card it's inserted, it can't be reseted, so nothing is going to work, I cant read neither write due it hasn't been reseted to spi mode. But if after the power on I extract the card from the MMC connector and insert it again, and later reset the pic to run again the program, the card it is mysteriously reseted and initiated OK:exclaim:, after that I can write and read.

Also if I switch off the 5V power of the system but not the 3.3V voltage supply of the card and after that I power on the pic to run the program, it reset the card ok. I tried also to switch off the 3.3V supply of the mmc when the system and pic it's running and after that to reset the pic to execute the test program and It can't reset the mmc, like the card was disconnected, but if I extract the mmc and connect it again, the program works as I said before.

So when I turn on the embedded system, if I want to use the mmc card I have to extract it and plug it again and reset the system. Thats really strange, any ideas??????

the code it's still the same, with the change that ckielstra pointed:

[Wizard]

It was me, I forgot to login before to post.

Waiting for any ideas ot information about the issue and mmc staff
_________________
Tomas L.

[ckielstra]

Looks like you have major problems in initializing the MMC card. Did you check out the thread mentioned by PCM Programmer? If you did you have noticed I'm not happy with the hardware design from that particular site. It's a quick-and-dirty design with some flaws in it and I don't feel like giving support on it.

Your program is incomplete, the file mmc_spi.c is missing.

[Wizard]

I know the interfacing circuit doesn't compile with the mmc specification, but I'm using the PIC18F4550 running on 5V. So I can't connect the mmc card spi lines directly with the pic pins with the pull-up resistors.
I have thought to use a inverter with open collector outputs (ie. 74LS05) with 1.8K resitors to 3.3V at the outputs. Any ideas?
_________________
Tomas L.

[C-H Wu]

Suppose PIN_B3 is TTL level input, then you don't need level translator.

#define MMC_DO PIN_B3

For the other pins, all you need is simple voltage divider.

#define MMC_CLK PIN_B1
#define MMC_DI PIN_B0
#define MMC_CS PIN_B2

For the power, I simply use two 0.7V diode like 1N4001 to get the voltage down to 3.6V from 5V with a 1 uF bypass capacitor.

It works fine for me.

Best wishes

[Wizard]

Thanks for the point, I think you mean that I dont need voltage divider in the #define MMC_DI PIN_B0 Line, which it's the data output of the MMC. That's how I have the circuit.

Thanks for the point of the diodes, I'll inform about any progress.
_________________
Tomas L.