Siemens S7-300

Hi guys
does anyone have any idea why this does not work with S7-300 siemens plc

OB81 : power Supply Fault

Network 1: Error of Battery, incoming event

L #OB81_FLT_ID
L B#16#22
==I
= M 81.1
L #OB81_EV_CLASS
L B#16#39
==I
= M 81.2

U M 81.1
U M 81.2
S M 81.0

Network 2: Battery ok, outgoing event

L #OB81_EV_CLASS
L B#16#38
==I
R M 81.0


regards

Matthew

I'm at home so can't verify, but I think OB81 is only reported in a S7-400 CPU.

OB81 is reorted in S7-300 CPU but

U. is not used ?

mj82

I see that you are using a compare (==) INT, but you are reading the event class from OB81 TEMP data which is in HEX.

You will have to convert the TEMP data to INT first then compare for the 'low battery' event.

Paul

mj82 - what does not work, the detection of the battery fault or the clearing of the battery fault ? Have you monitored OB81 and then disconnected the battery and viewed the CPU registers ?

I have downloaded your code into a 318-2DP (the battery has been "borrowed" from this CPU !), monitored OB81, restarted the plc and OB81 runs and sets M81.0 so it is working in my CPU.
As the battery is missing I can't re-connect to check the outgoing event.

Which CPU are you using ?

(NB: OB81 cannot be downloaded into a 317-2DP. I guess the new S7-300 MMC style CPU's don't have batteries and hence don't support OB81)

I have check, it is that. U is not an useble commarnd with the CPU that i am useing and is hilighlted in red when i tri to enter it ?

U is a german mnemonic - I used A instead.

SimonGoldsworthy said:

I have downloaded your code into a 318-2DP (the battery has been "borrowed" from this CPU !), monitored OB81, restarted the plc and OB81 runs and sets M81.0 so it is working in my CPU.

Click to expand...

Simon,

So are you telling me that everytime I have done this in the past I have not had to convert the OB81_FLT_ID to an INT for it to work?

The ==I will compare two HEX values then?

Paul

Paul,

the compare instructions (such as ==I at least) simply treat the contents of the accus as integers. Only if you're programming in LAD or FBD you have to move the hex values to integers OR you have to disable the type checking in the LAD/FBD editor (Options - Customize - select LAD/FBD tab - uncheck 'Type Check of Addresses'). But: do remember, if you're comparing hex values, that everything from 8000h on upwards to FFFFh will be treated as negative numbers.

Kind regards,

Jean Pierre

Thanks for the reply, as I only ever program in LAD, that would explain why I have had to convert each time.

I used to do a lot of STL when I programmed Step 5, I couldn't stand it then, so I tend not to use it now unless I really have to.

That's another little difference between STL and LAD to store in the back of the ol' grey matter.

Paul