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AG-BASRTB00-BD0 Page 16

Application Guide — BASrouters

T R L SO

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

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BASautomation 1
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