S7 Mmc


Join Date
Feb 2006
Jablonec nad Nisou
Hi every body,

last two weeks I was working on understanding what are S7-31x MMCs. In the end I collected following information

64KB-4MB SIEMENS MMC cards are standard 16MB MMCs with special SIEMENS format. Datasheet at http://www.tischer.cz/HB28D032MM2-RENESAS.pdf.

8MB SIEMENS MMCs are the same but 32MB MMCs.

You can make bit copy of these MMCs by using tools at http://personal.telefonica.terra.es/web/suwe in standard MMC/SD card reader. By using this tools you also copy the special SIEMENS format.

But in case you would like to use non SIEMENS 16MB or 32MB MMC, you cant use it in S7 as every MMC has private CID and CSD register where are stored informacion as OEM/APPLICATION ID, PRODUCT NAME, .... . The example of SIEMENS 64KB MMC is at http://www.tischer.cz/64kb.txt. CID is OTP register and first 14 bytes of CSD are programed only by manufacturer. S7 checks and compares stored info. from CID and CSD.

If you have SIEMENS MMC accidentaly formated in standard MMC/SD card reader/writer (for example as FAT format) you can repair it in this standard MMC/SD reader/writer.
1. read original SIEMENS MMC by S7imgrd (the same size as failed card)
2. write this image to failed MMC by S7imgwr

When I was analyzing MMCs I also find out how is the password stored at the MMC.

If you have any question, email me at [email protected]


Im try this up operation with MMC card. But without any success.

Card MMC
64kB equal number

Read and write functian with success, but PLC not recognite the MMC card
Im think the problem is not correct format of MMC card.


Try this:

  • 1.Read the image from original card
  • 2.Write this image to the wrong card
  • 3.Read the image from wrong card
  • 4.Compare images from the original and wrong cards.

If the images are the same, send me the image from wrong card and the the part number of this card and I’ll look at it.

Regards Petr
New procedure


I'm sorry, I have made mistake in description, if you need to make true bit copy of MMC card or you want to repair failed MMC card, you have to use WinHex program (http://www.x-ways.net/winhex/index-m.html).

Here is a procedure:
a) read the original MMC in 2 steps
1. http://www.tischer.cz/mmc1.jpg
2. http://www.tischer.cz/mmc2.jpg

64KB image http://www.tischer.cz/64KB.zip
8MB image http://www.tischer.cz/8MB.zip

b) write the original image into failed MMC
1. http://www.tischer.cz/mmc4.jpg
2. http://www.tischer.cz/mmc5.jpg
dont you afraid if you receive the following notice
3. http://www.tischer.cz/mmc5.jpg

!!!! S7imgrd and S7imgwr don't make true bit copy of MMC!!!!

[email protected]
password protection

I'v received lots of e-mails with question how is the the password stored at MMC. At the moment I don't want to public this information but if you send me per e-mail copy of the MMC made by WinHex, I send you the password FOC.

e-mail: [email protected]
So if i understand u correctly, it means we must always use the MMC card provided by Siemens. Other normal MMC made by WinHex is also not possible to use on the Siemens PLC. Correct?
You are right, but you can use MMC from other manufacturer if CID and CSD records in the MMC match the SIEMENS CID, CSD records.

64KB-4MB SIEMENS MMC cards work on the same hardware (16MB MMC), 8MB SIEMENS MMC are 32MB MMC.

You can't copy format from 4MB card to 64KB as 4MB and 64KB cards work at the same hardware because have diferent CID records.

S7s recognise MMC size from CID, CSD and card format. All these three records must match.

CID and CSD records are OTP (one time programable by manufacturer)In CSD register last 8 bits and CRC are partialy user programable.

I have made my oven CID and CSD card reader/writer and have programed simple C++ program as I hadn't been able to find any standard MMC reader with posibility to read and write CSD register.

At the moment I look for any china supplier who will be able supply me with the MMC programed as SIEMENS MMC. If I am succesfull, the price of 8MB MMC will be about 40-50 USD.

Last edited:
4 --> 2MB

You can use 4MB image for 2MB card. The part, where is stored information that the size of the card is 2MB is write protected and the rest of the format is the same for both cards.


I have tried it. However unsuccessful...

To-size image of 64KB card is working perfectly.
Both cards (64KB and 2MB) were accidentally FAT formatted.
So my last cast is 2MB card image.

Please help me.

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