Appendix 2
APRILAIRE COMMAND SET
SN# [Command] [? or =] [Value (use with = only) ] 
Enter
A full command set and detailed explanation of the command set is available for those who want to write their own software. Contact Research Products Corporation at
Upper or lower case letters may be used for all commands. Invalid characters will immediately invalidate a command, so the use of backspace or delete is not allowed (applies mainly when interacting with the thermostat using HyperTerminal).
All commands will begin with the characters SN. Immediately following the SN, without any intervening spaces (blanks), will be the address (#) from 1 to 64 of the Model 8870 Thermostat with which you are communicating.
Single digit addresses may be sent as a two digit address with a leading zero. Omitting the address, or using a 0 (zero) in place of a space makes the command global, and all connected thermostats will respond. Following this initial command sequence, spaces may be inserted at this point
only, for clarity between commands. The next portion is the command or variable [Command]. The table on page 20
describes the basic commands. The next portion [? or =] is the action to be performed: “?” corresponds to “state your value” while “=” corresponds to “set your value”. Spaces
are allowed between the command and the action. The final portion, [Value], is used only if a command or variable is
to be set. The value must follow the action with no
intervening spaces. A 
Enter is used as the terminator for the command string. Line feeds (LF) should not be sent with commands as this is a recognized ASCII character and invalidates any command received between the line feed and the next carriage return.
EXCEPTION: The command SN? or SN0? will respond with all connected thermostats returning their address.
COMMAND RESPONSE SYNTAX
The Model 8870 will respond by supplying the information requested or by confirming the completion of an action command. The response syntax is generally the same as that used for commands, but no spaces separate command, action or value. Responses are sent in upper case ASCII format. Should a command not be recognized, no response will be forthcoming – there is no ERROR message.
Unless otherwise noted as “Read Only” or “Write Only”, all commands are “Read and Write”.
Inquiries can be made with all commands (with the exception of BLTON) to determine the existing value of a variable. Inquiry is done using the following syntax:
SN [address number, or <blank> or 0 (zero) for global] “COMMAND” ?; where command is the variable whose value is desired.
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