A program in bCX or b3 is writing/reading to/from a second device, the write/read operation is not working and the second device is not listed on the list of known devices in the bCX/b3 that has the program.
- BACnet bCX
Device is not answering to WHO-IS message.
When a reference is made in a device (A) to a second device (B) a WHO-IS message is sent from A to B, when the I-AM is received the devices is added to the list of known devices.
If no I-AM is received then the device remains unknown and cannot be listed, as a consequence write/read messages (among other things) will fail.
In the screen shot below device b3.810 know about itself and one other device (b3.867).
If a program in b3.810 performs a WriteProperty operation to a third device C, the WriteProperty operation can not succeed until C has been added to the list of known devices via the internal mechanism explained above.
Use Wireshark to check whether the device with the reference is sending out the WHO-IS and more importantly whether an I-AM is coming back from the destination device.
In the case that originated this ticket, the destination third party device would not consistently send an I-AM when operating at high baud rate, the MSTP baud had to be lowered to 19200 .