Wago 750-636 DC-Drive Controller always shows current position = 0

[moniwe]

For Eclipse 4diac I try to support 750-636 DC-Drive Controller for its modular IO implementation. The motor I connected for testing is a encoder motor used within a Fischertechnik plant. With my current implementation I am able to move the motor in positive and negative direction but the current position remains 0.

TForteByte inDataDWord[4];  
int retval = mAppDevInterface->ReadBytes(mKBusDeviceId, mTaskId, mInputOffset, 4, inDataDWord);

mAppDevInterface->ReadBytes returns DAL_SUCCESS. Has someone an idea what could be wrong that the current position remains 0?