Max Master is a MSTP data packet management concept that has been around long before BACnet was ever developed.
A very common cause of EIA 485 MSTP (Master-Slave-Token-Passing) discovery failure, is that one or more of the devices
(Masters) on the MSTP Buss, has their internal "Max Master" setting at a number that does not match all of the other device
"MaxMaster" settings. If you want effective token passing, all devices on the buss need to have the same
Max Master value put into their configuration settings.
Many manufacturers ship their MSTB devices with the default Max Master setting at 127 (the max number for the MSTP
device addresses on a MSTP buss). If you have only 10 devices on you buss, this default setting of 127 can slow you buss down.
I have seen some "out of the box" MSTP devices that have it default at zero. This will cause problems.
I would say, give a check of all you MSTP devices on you buss to make sure they are all set to
the same number, and that Max Master number would be the highest address plus 1.
If you want a faster buss, keep all you addresses in order, without gaps (1,2,3,4,5,6, etc)
Hope this helps.
By the way, BACnet did not design or develop any of the electronic comm busses that their BACnet data packets
and protocol ride on. They just created data sharing rules that allow BACnet data packets to co-exist within
the minimum functional requirements of the underlying electrical buss requirements.
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