RMA
Member
Hi guys, better late than never,
Well, we're discovering all sorts of interesting things here, but I'm having difficulty deciding how to arrange them in order of importance - in fact I think I'll leave that to Jesper, as he'll do a better job than me, because of his greater experience and more detailed as well as wider knowledge of S7. (grovel, grovel!)
For me the most important thing is the discovery that there is no such thing as a S7-3xx CPU - they are all different! And not just as Siemens would have us believe, between Firmware V1 & V2. Jesper doesn't say (or I missed it) which Version Firmware his 313C has, but it really doesn't matter, because neither of my CPUs react the same way his 313 does i.e. it apparently saves the the current actual value, during the first power fail - I would hope it also does it during the first OFF-ON cycle (did you try that Jesper?), otherwise some people are going to get an unpleasant surprise some day.
Come to think of it that may be the most important thing of all - when you get a new MMC 3xx CPU, play with it immediately to find out under what conditions it saves what it considers to be the Initial Value of the DB to the MMC!
Next Point - Prize for the most misleading nomenclature of all time must go to Siemens for the "Initial Value" field when creating a DB - as you can see on the next post, it's not used anywhere - that's right, nowhere, under the conditions under which I tested!
To be considered if you're playing around a lot before doing your final project on a used MMC - get yourself a prommer so that you can see - and delete - what's on it. Otherwise if you create a DB for your new project, it's Initial Value will remain the Initial Value that was generated when the DB with that number was first created - which might be something quite different from what you were expecting!
I've included a bit from the Siemens handbook describing how V2 handles the DBs, if you take it at face value and think that the value you entered in the Initial Value field is what you'll get from a non-retentive DB, you're in for a big surprise if you didn't also set it in the "Actual Value" field on creating the DB! Unless of course, your CPU behaves like Jespers!
Once again, apologies for the widescreen, but it was barely legible at 800x600.
Well, we're discovering all sorts of interesting things here, but I'm having difficulty deciding how to arrange them in order of importance - in fact I think I'll leave that to Jesper, as he'll do a better job than me, because of his greater experience and more detailed as well as wider knowledge of S7. (grovel, grovel!)
For me the most important thing is the discovery that there is no such thing as a S7-3xx CPU - they are all different! And not just as Siemens would have us believe, between Firmware V1 & V2. Jesper doesn't say (or I missed it) which Version Firmware his 313C has, but it really doesn't matter, because neither of my CPUs react the same way his 313 does i.e. it apparently saves the the current actual value, during the first power fail - I would hope it also does it during the first OFF-ON cycle (did you try that Jesper?), otherwise some people are going to get an unpleasant surprise some day.
Come to think of it that may be the most important thing of all - when you get a new MMC 3xx CPU, play with it immediately to find out under what conditions it saves what it considers to be the Initial Value of the DB to the MMC!
Next Point - Prize for the most misleading nomenclature of all time must go to Siemens for the "Initial Value" field when creating a DB - as you can see on the next post, it's not used anywhere - that's right, nowhere, under the conditions under which I tested!
To be considered if you're playing around a lot before doing your final project on a used MMC - get yourself a prommer so that you can see - and delete - what's on it. Otherwise if you create a DB for your new project, it's Initial Value will remain the Initial Value that was generated when the DB with that number was first created - which might be something quite different from what you were expecting!
I've included a bit from the Siemens handbook describing how V2 handles the DBs, if you take it at face value and think that the value you entered in the Initial Value field is what you'll get from a non-retentive DB, you're in for a big surprise if you didn't also set it in the "Actual Value" field on creating the DB! Unless of course, your CPU behaves like Jespers!
Once again, apologies for the widescreen, but it was barely legible at 800x600.