SYSTEM INTERFACE
The System Network communication interface is a non-isolated, 4-wire, full-duplex RS-485 communication link. The ‘A’ terminals are transmit
(reference automation system) and the ‘B’ terminals are the receive pair (reference automation system). The baud rate is 9,600 bps by default.
It can be changed using the user interface (See Setup Screens) or through a command from the Host controller. When the baud rate is changed,
the protocol timing is scaled as well.
TIMING AND SYNCHRONIZATION
The protocol uses time division multiple access (TMDA) to allow each node to have exclusive control of the receive lines of the Host controller
for a specified duration.
The communication frame is divided into a maximum of 64 time slots. The number of time slots are based on the setting for number of
thermostats on the network. The default setting is 64. Each slot is divided into four sub-slots. Legacy timing is based on 16-bit timer running at
1MHz (e.g. 65536 * 1/1MHz = 65.536 ms).
Baud Rate Slot Width Sub-slot Width
9,600 262.144 ms 65.536 ms
19,200 131.072 ms 32.768 ms
The four sub-slots of a slot are:
Sub-slot Name Description
1 Solicited Response Sub-slot For a node to respond to a Host command
2 Unsolicited Message Sub-slot For a node to send an unsolicited message to the Host
3 Expansion Sub-slot 1 Reserved
4 Expansion Sub-slot 2 Reserved
The following figure depicts the communication frame and slot divisions. (NOTE: Timing shown is for 9,600 bps and is rounded for illustrative purposes.)
Communication Frame
Slot 1 Slot 2 Slot 3 Slot 4 Slot 5
•••
Slot 63 Slot 64
262 ms
Solicited Response Sub-slot Unsolicited Message Sub-slot Expansion Sub-slot 1 Expansion Sub-slot 2
65 ms
65 ms
65 ms
65 ms
Slot
2
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Thermal Specifications
Weight and Dimensions
