Contemporary Control Systems BASrouter Application Guide - Manual (Page 16)

AG-BASRTB00-BD0 Page 16
Application Guide — BASrouters
C
ONTR LS O
®
CONTEMPORARY
BACnet MS/TP is short for BACnet over a master/slave
token-passing network. Stations that support the
token-passing protocol are called masters while stations
that do not support the token-passing protocol are called
slaves. This is oftentimes confusing. The master with
the token has momentary control over the network.
This station can basically send a message or pass the
token to its logical neighbour — the station with the next
highest address. Master addressing begins at zero
and can go up to 127. Once the token reaches the
master with the highest address, that master passes the
token to the station with the lowest address. So if a
slave device does not participate in the token passing
process, how can it be reached? The answer is a slave
proxy which the BASrouterLX supports.
Slave devices need to be assigned to a slave proxy and
there are two ways of doing this — manual and auto
discovery. If you know the particulars of the slave
device you can enter the data manually by checking the
Slave Proxy Enable on the Advanced — Slave Proxy
screen and then clicking Apply. Next enter the data for
each slave device. You will need to know its MAC
Address, Device Instance, Vendor ID and Max APDU.
Unlike master devices, slave addresses can range from
0 to 254. These values had to have been set in the
slave device previously. This information is simply
transferred to the slave proxy. Once the entries are
made the Apply button is clicked. This data will appear
in the Slave Proxy Table as an entry. Individual entries
can be deleted by entry number.
The second approach to registering a slave device is
auto discovery. Check the Auto Slave Enable box and
then click Apply. The View Auto Slaves button will then
become active. Clicking on this button begins the
automatic discovery process which can be lengthy. The
results of the discovery process will appear in the Slave
Proxy Table as above. Individual entries can be
deleted by entry number.
Once a slave device is registered with the slave proxy,
communication to the slave is possible.
Application #11 — Proxy Support for MS/TP Slave Devices
BACnet MS/TP Network 2007
BACnet/IP Network 1
128