OK still investigating some of our issues. It is my understanding that with J1939, Upon start-up you should make a "Request for Address Claim Message" which the PV750 is doing. However It is my understanding that you have to wait for 250 ms to allow the other unit to respond. In the trace below recorded on our system were we do not seem to wait only 95.8 ms:

• 313) 11258.4 Rx 19FF0104 8 60 0F 32 99 00 F1 00 00
  314) 11259.0 Rx 19FF0104 8 61 1A 1A 00 E1 04 00 00
  315) 11259.6 Rx 19FF0104 8 62 00 00 FF FF FF FF FF
  316) 11263.7 Rx 18EAFFFE 3 00 EE 00
  317) 11268.6 Rx 18EEFF04 8 01 00 40 26 00 01 C8 C0
  318) 11358.4 Rx 19FF0104 8 80 0F 32 99 00 F1 00 00
  319) 11359.0 Rx 19FF0104 8 81 1A 1A 00 E0 04 00 00
  320) 11359.5 Rx 18EEFFF2 8 7A 6B C3 09 10 A0 A0 C0
  321) 11360.1 Rx 19FF0104 8 82 00 00 FF FF FF FF FF
  322) 11458.4 Rx 19FF0104 8 A0 0F 32 99 00 F1 00 00
  323) 11459.0 Rx 19FF0104 8 A1 1A 1A 00 E0 04 00 00
  324) 11459.6 Rx 19FF0104 8 A2 00 00 FF FF FF FF FF

In this case, the other unit did respond within 9 ms so everything went well. However in the following case where we purposely had created an address conflict, the other unit does not seem to be able answer before you make your address claim:

• 193) 8987.6 Rx 19FF0101 8 80 0F 32 99 00 F1 00 00
  194) 8988.2 Rx 19FF0101 8 81 1A 19 00 F7 04 00 00
  195) 8988.8 Rx 19FF0101 8 82 00 00 FF FF FF FF FF
  196) 20397.2 Rx 18EAFFFE 3 00 EE 00
  197) 20493.2 Rx 18EEFF01 8 7A 6B C3 09 10 A0 A0 C0
  198) 21400.2 Rx 18EAFF01 3 01 F8 01
  199) 21565.2 Rx 18EAFF01 3 02 F8 01
  200) 21732.2 Rx 18EAFF01 3 03 F5 01

In this case the other unit did not respond to the request for address claim yet the VP750 is proceeding with the "address Claim" message within the same time window. Is this normal? Am I mis-understanding the 250 millisecond requirement?

The first message is a request for address claim. We send this message so that we can use it to enumerate devices that we are listening for based on the NAME, rather than source address.

The second message is the address claim, the 250 mS time should start after this message is transmitted. At this point a device with higher priority may send its own address claim to force us to another address. If a lower priority device sees our address claim, it should send a new address claim for a different address, or transmit a can't claim message (address 0xfe).

The timing of the two messages is unrelated, and to a certain extent is random. We transmit the first message as soon as we can, we transmit the second message based on a random delay from power up. We are following the NMEA state machine and procedure for address claim, which is slightly different, but compatible with J1939.