User Guide

ViewStat Programming Protocol

ViewStat Communicating Thermostat - Programming Protocol Reference Guide

ViewStat Programming Protocol

You can program the Viewstat to perform a wide variety of operations using SEND_STRING

commands. The Viewstat is designed to automatically echo each command you send to the

thermostat. For example, if you send a

SEND_STRING HVAC "'SN9 SCALE?',13" command, the

system automatically echoes

SN9=SCALE?. Then, the system will generate a reply when the

operation is complete that shows the current temperature scale. This section contains timing and

command descriptions, and lists communication control and thermostat commands.

For most applications, the NetLinx module for the ViewStat can be used, eliminating the need to

manually generate any code at all for the ViewStat. For detailed information on using the module,

refer to the ViewStat Communicating Thermostat Instruction Manual ("Using the NetLinx Module"

section), available on the AMX.COM web site.

Network Communication

Network communication is non-isolated, full duplex RS-422 using 4 + 1 wires. The 'A' terminals

are the transmit pair while the 'B' terminals are the receive pair. This nomenclature uses the host

computer as the reference, so transmit refers the lines on which the host transmits data to the

thermostat while receive refers to the lines on which the host receives data from the thermostat.

ASCII-based firmware, which is fully compatible with the StatNet command set, is defined below.

Up to 64 uniquely addressed devices are allowed on the network.

There are three response mechanisms depending on the nature of the command request:

! Explicit Address Commands

! Global Address Commands

! Unsolicited Responses

Explicit Address Commands

Explicit Address Commands are those commands that specify a single, particular address in the

command header (i.e.

SN13 MODE=OFF). As this command is transmitted down the RS-422 bus,

each device connected will receive it into their buffer. The command will begin to be interpreted by

each device. Once the address is scanned, the entire command will be discarded if it is not that

unit's address. The unit that was explicitly addressed will complete the interpretation of the

command, act on it, and respond back to the host. Responses from an explicitly addressed

command can begin as quickly as 20 milliseconds after the command was sent, and not later than

330 milliseconds.

To communicate with the control system, set the baud to 9,600, data bits to 8, parity

to none, and stop bits to 1.