Why are the TP/XF-1250 transceiver parameters different between a neuron 3150 and 5000 deivce? (KB1040)

Comparing the Nodeutil reported TP/XF-1250  transceiver parameters with those of a 3150 designs, there are subtle differences. Notably that on the 3150 design Nodeutil reports:

Preamble length = 150.6 microsec

Packet cycle = 4020 microsec

Beta 2 control = 24 microsec

Transmit interpacket = 0 microseconds

Receive interpacket = 0 microseconds


But on the 5000 you get

Preamble length = 142.5 microseconds

Packet cycle = 4020 microseconds

Beta 2 control = 24 microseconds

Transmit interpacket = 172.2 microseconds

Receive interpacket = 184.5 microseconds


Why are there differences in the Transmit and Receive Interpacket timings? Does this mean that a 3150 design will not communicate with a 5000 design?


Answer: The two types of devices do interoperate. The difference is down to the way Nodeutil reports the parameters.

The values of the transmit and receive interpacket gaps for the 3150 device are classed as the base timings and thus show up as a zero in Nodeutil. These timings are set by the MAC CPU that deals with layer 2 and layer 1 (the physical layer) but does not mean there is no interpacket padding, just that we don't show it due to a Neuron 3150 usually operating with a input clock crystal of 10Mhz being classed as the base standard.

If you go up in frequency and put a 20Mhz crystal on a 3150 and set the device template appropriately in Nodebuilder, there will be padding. If you do this then you should see the same values as the neuron 5000 running at a 80Mhz system clock.

It is simply that Nodeutil 3.23 does not report the values of base time plus padding or total times for a 3150 at 10Mhz.

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