Memory card Requirement to access DP Slave registers

Hi guys,

I have an older 315-2DP (6es7-2af03-0ab0) with which I am trying to communicate with a hilscher type gateway that is a profibus slave.. This has the function to deliver 32 words of PLC data to a Modbus master.

After setting up communications and running without bus-faults, I observe that the DP slave's registers aren't getting written upon.

In the Hardware configuration I have assigned QW 40- QW 103 as the Profibus-slaves registers, configured as output of the PLC.

Is this happening because there is no memory card?

Thanks for your response.

The Memory-card I ask about is regarding the CPU itself. At present, there is none. My question is whether the MMC card is essential.

The DP-slave is only a hilscher type Gateway Converting Profibus to Modbus.

I tried a second experiment. When I use a later version  CPU-3152DP ie 6ES7-315-2AG10-0AB0, I observe that the CPU needs the micro-memory card (I used 64 kB) to communicate with the DP slave, or even download to it! With the 64 kB card, there is no problem. The slave communicates perfectly.

In the case of the older PLC-6 Es7 315-2Af03-0AB0 I'm able to download & there is no bus-fault and when I go on line I observe that the IW/QWs of the DP-slave dont get read or written.

BTW, can you tell me whether I need to use profibus telegram functions like DP-R & DP-W for Reading & writing from to the slave's registers.?

Hello Raj;

You are working with a CPU that was taken out of production in 2004, I am glad to see that it seems to be working correctly 15 years later.

You should take a few seconds to look at this description of the way the S7-300 memory concept has evolved over the years; in the document attached, your CPU would be covered by Case 3. It has an integrated RAM of 96 kB as Load Memory (see the image below), so you do not need a memory card to download your program to the CPU; however, you need battery support to maintain that memory area when you power off the unit. Using a memiry card as Load memory will simply give you mainteenance of the program memory without a battery.

How can you obtain an overview of the memory concept of SIMATIC S7-300 CPUs and C7 devices?

https://support.industry.siemens.com/cs/us/en/view/7302326

As per the description of the CPU in the attachment below, it can act as a Profibus-DP master (or slave) through its integrated Profibus port, so you should be able to connect to your Profibus slaves if the integrated port, the network cabling and the Profibus configuration are working.

I suggest you take and attach a screenshot of the Hardware Configuration showing us the Profibus slaves and the input/output addresses used for Profibus exchanges; also give us some idea of how you are addressing these slaves in your program.

Hope this helps,

Daniel Chartier

Thanks a million, it saved me some money and headaches:-), to realize that one does not need a memory card for AF03 era CPU to talk with DP slaves!

Finally, we got it to work. The issue related to choice of correct DP-ID, which is of course something that is out of Siemen's scope. We were using an Indian-made Profibus-Modbus Gateway made by Renu Electronics. In India, this is quite widely used and the 315-2DP is the most popular PLC still!

There are 2 Screenshots are attached here Before and After solving the issue.

Thanks for your prompt guidance