Siemens MRES option

I have years of experience with A-B and am now troubleshooting an S7-300 Siemens with Profibus. I'm told that it was running fine, stopped and is indicating faults...SF and BF red LEDs on the processor, the coupling module and the Profibus connector where it plugs into the processor.. I have been researching threads online along with Siemens Manual and seem to be getting conflicting info. First question: What exactly is the MRES option. This one is a momentary PB integral with the run/stop switch. Does it clear the memory and delete the program OR does it reset a fault, (if it can reset it), and try to re-start the processor from a memory card or eeprom or ????? This is a machine that has been mothballed for years with no original personnel available. Also. If this equipment is over 12 years old, will it communicate with windows 7 or newer OR must it be windows XP? We do not want to chance losing the program until we're sure we can communicate with laptop. Any help would be greatly appreciated. Thanks so much.

Link to the CPU manual here: https://cache.industry.siemens.com/dl/files/591/8860591/att_105766/v1/HB_CPU312IFM_bis_318-2DP_e.pdf


Take a photo and post it so we can see what type of CPU you've got.

1) you can call Siemens tech support for help, FYI. I mention this because it often surprises guys with largely AB experience. They don't require a support contract, although they do charge for support for legacy products or support outside of 8-5 in your local time zone. S7-300s are current products, although they are on the way out.

support.industry.siemens.com or 800-333-7421


2) My understanding is that MRES will wipe the work memory of the PLC and then restart by copying everything again from the memory card (if one is present). Things like the diagnostic buffer and basic communication parameters like Profibus address are not affected, but retentive memory and any configured connections are.


MRES MIGHT reset a fault, but only in the same way that turning any electronic device off and back on would.


The BF light stands for Bus Fault. If it is lit in a number of places, then I'd recommend troubleshooting the Profibus network.


Current versions of Simatic Manager (Step 7 v5.6) support up to Windows 10, and I've never seen a project that was too old to open. You will need a Profibus adapter to connect to the CPU if the CPU doesn't have Ethernet available.

Thanks so much for the info. I should be there tomorrow to get a pic to send.

Micheal
My two cents
I echo the above
I wouldn’t do the reset with the switch
Sounds like a profibus node is offline
See if you can find the node that is offline and go from stop to run with the switch.
It’s difficult without the software or a way to scan the profibus network or no diagnostic in an hmi etc
With just the switch and not a key switch , it’s the newer cpu

The S7-300 can communicate fine with Win 7 and Win 10. It is the software on the windows PC that must be compatible with the Windows version.


MRES will do 2 different things depending on the status of the hardware configuration on the flash card.
If there is a valid hardware configuration, then MRES merely resets the actual values in the program to the initial values defined by the programmer.
If there is no valid hardware configuration on the card, MRES will clear the memory.


All we know from your 1st post is that it is a newish S7-300 and there are SF and BF. That is not enough to determine what is the problem or what to do about it.

Please state the exact type no of the CPU as well as all other hardware in the rack.
Do you have access to the STEP7 programming software ?
Do you have access to the source STEP7 project ?