User Guide

PROGRAMMING Honeywell • 13
4.3 BACnet MS/TP parameter descriptions
4.3.1 BACnet MS/TP Parameters
P5.8.3.1.1 B
AUD RATE
Select the communication speed for the network. The default value is 9600 baud. If Autobaud-
ing is selected, the node will detect the baudrate. There must be at least one device in the bus
to select the baud rate and to start token transmitting. When the baudrate is detected, it is
saved into this parameter.
NOTE! Autobauding is disabled after baudrate is detected.
P5.8.3.1.2 MAC ADDRESS
The parameters of every device must be set before connecting to the bus. Especially the pa-
rameters MAC address and Baud rate must be the same as in the master’s configuration.
The first parameter, BACnet MAC (Medium Access Control) address, must be unique on the
network to which it is connected. The same MAC address may be used on a device on another
network within the internetwork.
Addresses 128-254 are reserved for slaves. Addresses 1-127 are valid for both masters and
slaves. The portion of the address space that is actually used for masters in a particular instal-
lation is determined by the value of the Max_Master property of the Device object.
It is recommended that MAC address 0 be reserved for use by the MS/TP router. 255 is re-
served for broadcasts.
P5.8.3.1.3 I
NSTANCE NUMBER
The Device Object's Instance number must be unique across the entire BACnet internetwork
because it is used to uniquely identify the BACnet devices. It may be used to conveniently iden-
tify the BACnet device from other devices during installation.
If 0 (default) is selected, the Device Instance number is generated from the last 22 bit of the
Ethernet MAC address. This unique number is then shown in the Monitor menu (actual in-
stance).
P5.8.3.1.4 M
AXMASTER
This parameter defines the last possible master on the network segment. Each master node is
responsible for searching new devices from network using the ‘poll for master’ messages. The
nodes are searched up to MAC address defined by MaxMaster parameter.
This parameter affects the cycle time of the token. We recommend to use the highest MAC ad-
dress value in the network for this parameter.
P5.8.3.1.5 COMMUNICATION TIMEOUT
The BACnet MS/TP indicates timeout error if the node is not receiving a token within time de-
fined by this parameter. It can be used to detect communication loss to other nodes. Time unit
is seconds.
NOTE! Application parameter P3.9.1.6 (ID 733) can be use to define action for communication
timeout.