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• RS-485 half duplex

• 8n1

• DATA0...n transmitted unchanged, low nibbles are BCD (0-9)

• ADDR byte and CSUM byte split into two bytes each, hi and lo nibbles might be split between the two bytes, however I'm confused as to why it appears that the ADDR byte is a start flag byte. sub_ADDR matches the protocol specification.

• One-way communication

• FEC appears to be "repeat the message" as all packets are immediately duplicated in the recorded stream, i.e. 1,1,2,2,3,3..etc.

• Receiver likely "pretends it never happened" if packets are mangled as past data is irrelevant

• (EDIT) All packets are of known length and the lengths do not change in the data set

• (EDIT: CRITICAL INFO) Low nibbles of bytes labeled A3-A6 and B3-B6 represent digits 0-9 as BCD. A value of 0x0f would blank the digit on the display.[1] Therefore:

   0a 0c 02 00 60 00 80 0b -> "20:00"
   28 0c 02 00 60 00 80    -> "20:00"
   0a 0c 01 09 65 09 d8 0b -> "19:59"
   0a 0c 0f 09 65 09 80 0b -> " 9:59"
  

• (EDIT) High nibbles of A3-A6 contain flag bits. Known flag bits include bit 6 in DATA2 (A5,B5) which indicates state == running, and bit 5 in DATA2 (A5,B5) which indicates colon == on.

• RS-485 half duplex

• 8n1

• DATA0...n transmitted unchanged, low nibbles are BCD (0-9)

• (EDIT) this is likely not the case, as the spec I have does not seem to be the correct one. Disregard the following point. ADDR byte and CSUM byte split into two bytes each, hi and lo nibbles might be split between the two bytes, however I'm confused as to why it appears that the ADDR byte is a start flag byte.

• sub_ADDR matches the protocol specification, used to identify the data in the packet to a specific part of the display, and possibly to different displays

• One-way communication (EDIT) one-to-many master-slave likely

• FEC appears to be "repeat the message" as all packets are immediately duplicated in the recorded stream, i.e. 1,1,2,2,3,3..etc.

• Receiver likely "pretends it never happened" if packets are mangled as past data is irrelevant

• (EDIT) All packets are of known length and the lengths do not change in the data set

• (EDIT: CRITICAL INFO) Low nibbles of bytes labeled A3-A6 and B3-B6 represent digits 0-9 as BCD. A value of 0x0f would blank the digit on the display.[1] Therefore:

   0a 0c 02 00 60 00 80 0b -> "20:00"
   28 0c 02 00 60 00 80    -> "20:00"
   0a 0c 01 09 65 09 d8 0b -> "19:59"
   0a 0c 0f 09 65 09 80 0b -> " 9:59"
  

• (EDIT) High nibbles of A3-A6 contain flag bits. Known flag bits include bit 6 in DATA2 (A5,B5) which indicates state == running, and bit 5 in DATA2 (A5,B5) which indicates colon == on.

(EDIT) UPDATE: You know, the more I think about it and look around the internet, this system shares many similarities with DMX protocol. This system was made to work with many devices daisy-chained together.

1. One-to-many connection, with termination required at the end
2. 0x00 break on every line, similar to lo value inter-packet (line?) break, bursts of data about once a second
3. possibly no error correction at all
4. used to control a "lighting" device (7-segment display)
5. others ...?

• RS-485 half duplex

• 8n1

• DATA0...n transmitted unchanged, low nibbles are BCD (0-9)

• ADDR byte and CSUM byte split into two bytes each, hi and lo nibbles might be split between the two bytes, however I'm confused as to why it appears that the ADDR byte is a start flag byte. sub_ADDR matches the protocol specification.

• One-way communication

• FEC appears to be "repeat the message" as all packets are immediately duplicated in the recorded stream, i.e. 1,1,2,2,3,3..etc.

• Receiver likely "pretends it never happened" if packets are mangled as past data is irrelevant

• (EDIT) All packets are of known length and the lengths do not change in the data set

• (EDIT: CRITICAL INFO) Low nibbles of bytes labeled A3-A6 and B3-B6 represent digits 0-9 as BCD. A value of 0x0f would blank the digit on the display. Therefore:

  0a 0c 02 00 60 00 80 0b -> "20:00" 28 0c 02 00 60 00 80 -> "20:00" 0a 0c 01 09 65 09 d8 0b -> "19:59" 0a 0c 0f 09 65 09 80 0b -> " 9:59"

• RS-485 half duplex

• 8n1

• DATA0...n transmitted unchanged, low nibbles are BCD (0-9)

• ADDR byte and CSUM byte split into two bytes each, hi and lo nibbles might be split between the two bytes, however I'm confused as to why it appears that the ADDR byte is a start flag byte. sub_ADDR matches the protocol specification.

• One-way communication

• FEC appears to be "repeat the message" as all packets are immediately duplicated in the recorded stream, i.e. 1,1,2,2,3,3..etc.

• Receiver likely "pretends it never happened" if packets are mangled as past data is irrelevant

• (EDIT) All packets are of known length and the lengths do not change in the data set

• (EDIT: CRITICAL INFO) Low nibbles of bytes labeled A3-A6 and B3-B6 represent digits 0-9 as BCD. A value of 0x0f would blank the digit on the display.[1] Therefore:

   0a 0c 02 00 60 00 80 0b -> "20:00"
   28 0c 02 00 60 00 80    -> "20:00"
   0a 0c 01 09 65 09 d8 0b -> "19:59"
   0a 0c 0f 09 65 09 80 0b -> " 9:59"
  

• (EDIT) High nibbles of A3-A6 contain flag bits. Known flag bits include bit 6 in DATA2 (A5,B5) which indicates state == running, and bit 5 in DATA2 (A5,B5) which indicates colon == on.

[1] "The Texas Instruments seven-segment display decoder chips 7446/7447/7448/7449 and 74246/74247/74248/74249 and the Siemens FLH551-7448/555-8448 chips used truncated versions of "2", "3", "4", "5" and "6" for digits A–E. Digit F (1111 binary) was blank." - wikipedia, 7-segment display