Query DeviceNet device for IO size prior to allocation of connection

G

Thread Starter

Gregory Ashmore

The DeviceNet allocation service (75; 0x4B) requires that certain device identity values, and the input and output data sizes, be entered into the device configuration structure prior to sending the explicit message.

Typically, we find the required information by running a diagnostic program supplied by the vendor of the scanner board. (The environment is PC-based control. But the problem is the same in any environment.)

I would like to discover this information by querying the various devices on the network. I have been able to discover which nodes (MacIds) are occupied, and I have used explicit messages to obtain the required values from the Identity object.

But I have not been able to obtain the IO sizes. The device will not provide the information because the connection [polled, btw] is not open. But I cannot open the connection in the usual way, because the allocation fails without the correct IO sizes.

It must be possible to discover the IO sizes--the third-party diagnostic tool does it. Does anyone know how it is done?
 
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