The i2cs Protocol

• All extended messages place a checksum byte in D14. For more details, see below.

• Wired i2cs devices must specifically be linked as a responder before they will accept commands (linking them only as controllers will not work). It is no longer possible to send direct commands to unlinked devices. (Uncertain whether this refers to all i2cs devices or only some.) If the device is not linked, it will return a NAK message (flag byte will be 0xAB). If you use an ALDB query command, an unlinked device will return only the address of each byte instead of its contents. (This restriction does not appear to apply to all wireless devices. Specifically we have seen motion sensors and triggerlincs that do not seem to have this limit.)

• After an i2cs device sends a group command, it will transmit a report of how many devices didn't respond with a cleanup message. This message appears to be a broadcast message with command1=01 (looks like Set Button Pressed) but command2=00 (for success) or unknown value for failure reports (possibly the number of failures?).

• It is possible to set how many times cleanup direct messages are set after a group broadcast. Also, previously any other Insteon traffic would cancel these messages. It is now possible to turn on a setting that forces a device to finish cleanup.

• x10 has been removed from some devices.

• The Get Insteon Engine Version command will return a value of 0xFF and a NAK if the i2cs device is not linked to the PLM. If it is linked, it will return a 0x02 which is the i2cs indicator.

• i2cs devices mostly do not support Peek/Poke. These were deprecated in i2 and now have been dropped from most devices. To edit the link table, use the Read/Write All-Link Database command (2F) instead.

• As with other aspects of the protocol, not every device supports every command.

• Many command that previously were sent as Standard messages now must be sent as Extended messages. These include Enter Linking Mode and device configuration commands for many devices including Insteon thermostats. For these messages, typically just fill in 00 for all the extended data bytes, but you do need the checksum byte (which is presumably the purpose of this change).

• Other changes I have yet to notice.

Linking

You can still programmatically link an i2cs that isn't already linked. This is necessary because of the second point above.

First put the PLM into linking mode:

02 64 [type] [group]

Where [type] = 00 if the PLM will be the responder, 01 if the PLM will be the controller, or 03 if the first device to go into linking mode will be the controller. [group] is the group number for the link.

Then send the command "Enter Linking Mode" to the recipient device as an extended message:

02 62 [address] 3F 09 [group] 00 00 00 00 00 00 00 00 00 00 00 00 00 [checksum]

Checksums

((Not(sum of cmd1..d13)) + 1) and 255