Clock Byte and System Byte - S7-300, TIA Portal

[ASF]

Hi all,

Got a new project with a Siemens S7-300 (CPU 312). I've just tried to copy in my motor control FB's from an S7-1200 project I did earlier in the year, and I've hit a speed bump in that my FB's use the "First Scan" tag from the system byte.

Now in the S7-1200, I selected which bit to use for the clock byte and the system byte, and the default tag table automatically created all the tags for first scan, always true/false, and all the pulsing tags.

In the S7-300, I can't find where to turn on the system byte, and though I've defined the clock byte, it doesn't show up in my tag table. So my questions are:

1. Does the S7-300 have a system byte available? If so, where do I activate it?
2. If not, is there another easy way of getting hold of a "first scan" bit without building my own?
3. How do I get the system byte (if it exists) and the clock byte to show up in my tag table?

Thanks!

 

[ASF]

bump

 

[JesperMP]

I dont know what the "system byte" is, but the "clock byte" is definitely there.
If you select a clock byte (MB0) for example, it does not automatically create symbols for the various bits M0.0..M0.7. You have to do that manually.
The 1st scan bit you have to make by yourself. Use OB100 to set the bit, and reset it in the end of OB1.

 

[ASF]

Thanks Jesper. From reading elsewhere, I found the same suggestion for creating a first scan bit - but there was also a caution that I may need to add my set bit to OB101 and OB102 as well - with each of those three OB's executing on a different type of restart (warm/cold/hot). But I can only seem to add in OB100 - do OB101 & OB102 not apply to the S7-300 312 CPU?

 

[mk42]

Thanks Jesper. From reading elsewhere, I found the same suggestion for creating a first scan bit - but there was also a caution that I may need to add my set bit to OB101 and OB102 as well - with each of those three OB's executing on a different type of restart (warm/cold/hot). But I can only seem to add in OB100 - do OB101 & OB102 not apply to the S7-300 312 CPU?

As far as I know, OB101 and OB102 are only for the S7-400. The S7-300 only does a warm restart, not a hot or cold.

 

[ASF]

Great, thanks!