User Guide

ViewStat Programming Protocol

ViewStat Communicating Thermostat - Programming Protocol Reference Guide

Multiple Commands

Explicit commands, to one particular thermostat, can be issued and acted upon with no more than

20 milliseconds between each command. Responses must be received before moving to the next

thermostat to issue commands. Global commands can also be issued with no more than 20

milliseconds between commands if the Command Response (

CR) has been set to Quiet (SN CR=Q)

or Silent (

SN CR=S). Responses, stationed in a buffer awaiting the opportunity to be sent, can

create a backlog and cause incoming commands to be disregarded. If global commands are to be

sent with the Command Response set to Normal (

SN CR=N), then the amount of time between any

set of two commands (the two commands must be separated by 20 milliseconds) must be 265

milliseconds times the "Number of Thermostats on the Network".

TIP: If responses are desired to a large number of commands, set the Command Response to Quiet,

send the commands (either globally or explicitly), then query individual thermostats (explicitly).

Return the command response to Normal when done. As an example consider a 64 thermostat

system. Now suppose the mode, fan, heat setting, cool setting and hold status were to be changed

on each thermostat. Further suppose that verification that all of these changes had been made were

required, and in addition the current temperature and remote temperature values were to be queried.

Using global commands, with the Command Response set to Normal, 17 seconds would be

required between each command. Five commands and two queries would be required (7 total

commands) requiring a total time of approximately two minutes.

Sending five commands and seven queries to each thermostat explicitly would require

approximately 37 seconds.

To maximize communication speed consider the following:

1. Communicate at 19200 baud

2. Do not skip addresses on the thermostat network unless absolutely necessary.

Global Command Sequence: Explicit Command Sequence

SN M=A SN CR=Q

SN F=A SN M=A

SN SH=70 SN F=A

SN SC=75 SN SH=70

SN HOLD=OFF SN SC=75

SN T? SN HOLD=OFF

SN OT? SN1 M?

SN1 F?

SN1 SH?

SN1 SC?

SN1 HOLD?

SN1 T?

SN1 OT?

SN2 M?

SN64 OT?

SN CR=N