User Guide

ViewStat Programming Protocol

ViewStat Communicating Thermostat - Programming Protocol Reference Guide

3. Set the "Number of Thermostats on the Network" to the highest addressed thermostat. If you

have only six thermostats address them 1 through 6 and set the highest address to six.

4. Only turn on the necessary change of state variables (COS - refer to the command

descriptions).

5. Send commands explicitly when possible.

6. When sending a large number of commands, set the Command Response to Quiet. If

responses are needed, explicitly query each thermostat on the network.

Network Override or Hold

Invoking Network Override causes the thermostat to disregard all received commands except

requests for data. This means that no response will be forthcoming. Network Override can be

invoked at the thermostat (by using the Enter button) or through the command set (

SN HOLD=ON).

Unsolicited data transmission is unaffected. Should the thermostat be receiving communication

when Network Override is invoked, the reaction will be carried out following the reaction caused

by the communication signal.

If receiving no response to a command will cause disruption to your program, then there are two

options: disable this feature or begin every command transmission by "

SN HOLD=OFF". To disable

the feature, ensure that Hold is "

OFF" at each thermostat and send the command "SN NETLK=1".

Alternatively it could be disabled through the Thermostat Set Up menu.

How to Detect When a Thermostat Has Gone Off-line

When a thermostat goes off-line (re-initializes) the Change of State (

COS) variables return to

default values -

OFF. The consequence of this occurring is that unsolicited responses will not be

sent by the thermostat (i.e. the automation system will not know when something has been changed

at the thermostat). There are two reasons that a thermostat will have gone off-line: the power had

been removed and reinstated or the Thermostat Set Up menu has been entered. When this occurs

the

COS variables must be reset. It is good practice to periodically check (once every 15 minutes is

a good start) that all thermostats are still responding. Simply query one of the

COS variables you

have turned on to verify it is still on. For example periodically send the command "

SN C2?". You

should receive the response "

SNx C2=ON"; where x is the address of each thermostat on the

network.