Siemens Snap7 communication, occasional status code reception normal but pose data empty


The log page shows that coordinate data has been sent, and the PLC end has received the corresponding status code, but the pose data displays as 0.


The PLC end implemented error prevention by periodically clearing the pose register. However, there is an occasional conflict between the timing of clearing and the vision system end writing pose data.

Troubleshooting Methods

  1. Set a unique automatic run step number for the operation of clearing the pose register, for instance, during the initialization phase of the image capturing cycle.
  2. If the “MM_Empty_Target” function FC is used, the method mentioned in “1” above should be applied (as shown below).

Note: Regarding function FC and INOUT interface definition, if FC is constantly enabled, it reads and writes interface parameters once every scan cycle. During the execution cycle when the pose is 0, if the visual end is writing pose data at this time, the data will be cleared.

  1. Investigate whether the “MM Interface” communication data block is being used as the overall INOUT interface parameters for the function block FB, and if this function block remains enabled. This is the same reason as mentioned in the above “2” prompt, leading to occasional conflicts with the visual end writing pose data.

Solution: For subsequent versions after 1.8.0, “Control Camera” and “Read Camera” structures will be added within the “MM Interface” communication data block, using the structure data as OUT interface parameters and IN interface parameters for the function block FB respectively (as shown in the picture below).