System mode:
Thermostat receiver
System mode receive space (bit 0) :
1.0mA at 12V
System mode receive mark (bit 1):
0.0mA at 0V
Thermostat transmitter
tri state: (off):
open collector, 0mA
System mode transmit space (bit 0):
2 V maximum at 4mA
System mode transmit mark (bit 1):
open collector, 0mA
PROTOCOL
The thermostat will respond to properly formatted messages from a polling device. The thermostat does not
initiate messages. The protocol is half-duplex, meaning that the thermostat does not receive while it is
transmitting. The host must not transmit while the thermostat is transmitting.
a. Byte format: 1 start bit, 8 data bits, 1 stop bit, no parity. LSB is transmitted first.
b. Data rates: 100, 300, 1200, 2400, and 9600 baud.
c. Message Format:
Byte 1:
Start/Remote Address
Bit 0-6:
Remote address (0 - 127, 0 = broadcast, 250 = universal address)
Bit 7:
1 for thermostat reply
0 for host message
Byte 2:
Data Length/Message type
Bits 7-4:
Data Length (0 - 15), invalid for ASCII strings.
Bits 3-0:
Message Type (0 - 15)
Bytes 3-n:
Data
0 to 15 bytes
Byte n+1:
checksum (add bytes 1-N to get checksum)
HOST TIMING REQUIREMENTS
a.
The host initiates polls. The host should not poll while a thermostat is transmitting.
b.
The thermostat will reply to a poll with a response.
c.
Thermostats do not reply to broadcast messages (remote address 0). Thermostats always respond
to address 250.
d.
A thermostat will not take action on, nor reply to a message with an invalid checksum byte. If a
thermostat does not reply, the host should try again after an intermessage timeout.
e.
Intermessage (between messages) timeout: 1.25 seconds. If a thermostat does not reply, the host
should wait a minimum of 1.25 seconds after the end of the host's transmission to retry the
message.
Copyright © 2008 Home Automation, Inc.
All Rights Reserved
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Summary of Contents for Omnistat2 RC-1000
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