Protocol details

Each message sent or received begins with a $ (hex 24). Messages end with a carrage return (\r / hex 0D).

Message types

Msg char	Hex value	Description
r	0x72	Get meter reading
j	0x6a	Join the meter
m	0x6d	Get mac address (of the MGM111)
i	0x69	Get install code
f	0x66	Get firmware version

Sending messages

Messages from the ESP to the MGM111 have just the previously mentioned $ starting delimiter, then a message type character and the ending \r delimiter. Each message is therefore exactly 3 bytes long. For example, to get the a mac address, send the hex bytes 24 6D 0D ($m\r)

Receiving responses

Response format bytes:

0	1	2	3	...	x
`$`	0x01	<msg type>	<payload length>	<payload>...	`\r`

Byte 1, 0x01 indicates that this is a response Byte 2 is the same messages type that was used to trigger this response Byte 3 is the length of the payload that follows Bytes 4+ are the payload of the response The final byte is the terminator

Ex:
24 01 6D 08 11 22 33 44 55 66 77 88 0D

Mac address response payload

The mac address reponse bytes are in reverse order, if the device responds with 11 22 33 44 55 66 77 88 then the mac address is 88:77:66:55:44:33:22:11

Install code response payload

The install code bytes are also swapped, see mac address response above

Meter reading response payload

Bytes	Meaning
0 - 3	Unknown, usually zeros
4 - 7	Watt hours consumed. Sometimes an invalid number greater than `0x0040 0000` is returned, which is not well understood
8 - 43	Unknown, seems to always be zeros
44 - 47	Unknown, seems to typically be `0x0000 0001`
48 - 51	Potentially a Watt-Hour to kWh divisor, typically `0x0000 0x03E8` (1000)
52 - 55	Unknown, typically `0xfbfb 0000`
56 - 59	Current watts being consumed
60 - 147	Unknown, usually zeros
148 - 151	Time in ms since the watt-hour value was reset to zero, big endian

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