S7 SFC 83 Read Time

Hi!

Impressed by the quality of this forum, I wonder if anyone knows an approximate time required to read (and write) with unlinked DB's using SFC 83 and SFC 84? Say 40 bytes or so. CPU 315-2.

I would guess there's a longer minimum time (especially for writing) and relative little extra per byte.

"System Software for S7-300/400 System and Standard Functions" does not say, and I can only find Volume 1.

Thanks
Jon

Hi,

You can find the block execution times in this document:

S7-300 Instruction List

Hi

The list of instruction times published by Siemens isn't very detailed on these SFCs. For your CPU all its says is "<950 μS" for SFC83 and "<900 μS" for SFC84. There's no indication of how much data this involves. The only additional information is that up to 3 concurrent requests are permitted. Both the 317 and 319 CPUs are quoted as "<300 μS" for both these operations.

I found the information at http://support.automation.siemens.com/WW/view/en/13206730

Regards

Ken

Thanks.

If you have a 315 available, program a loop and perform the processing say 100 times and measure the scan time increase.

I had one idea of capturing the system clock before and after, given that the elapsed time is less than roll-over and above the resolution. I believe the resolution is 10ms and I am already using the HW clock to get 1s flanks, so that would probably work too (if I loop a couple of times).