===== Venus and Loge protocol =====

Venus functions as a gateway between a local 485 network and a remote master which is connected via a TNC and radio.



==== Addresses ====
All devices including Venus have a system address. When a received TNC packet is not for Venus, the packet is forwarded onto the local 485 network. Responses from the 485 network are forwarded back out the TNC to the calling party.

  * 0x00 Downing Venus
  * 0x80 BB Venus
  * 0x81 BB Loge




==== Packet format ====
The packet format consists of:    
|**Offset** |**contents** |**description** |
|0      |0x7F     |Presynch1 |
|1      |0xFE     |Presynch2 |
|2 |0xaa |Destination address |
|3 |0xaa |Source address |
|4 |0xnn |packet data length |
|5 |0xpp |Opcode |
|6-n|0xzz|data bytes|
|z1|CRC Lo|CRC byte lo|
|z2|CRC Hi|CRC byte hi|


==== LOGE Status Packet format ====
|**Offset** |**contents** |**description** |
|0      |0x7F     |Presynch1 |
|1      |0xFE     |Presynch2 |
|2 |0xaa |Destination address |
|3 |0xaa |Source address |
|4 |0xnn |packet data length |
|5 |0xpp |Opcode |
|6|0xzz|Version Major|
|7|0xzz|Version Minor|
|8|0xzz|Inside T LSD|
|9|0xzz|Inside T MSD|
|10|0xzz|Outside T LSD|
|11|0xzz|Outside T MSD|
|12|0xzz|relays|
|12|0xzz|errors|
|z1|CRC Lo|CRC byte lo|
|z2|CRC Hi|CRC byte hi|

==== Opcodes ====
The following opcodes have been defined for the system:
|Opcode Val |Neumonic |Meaning|
| 0x02|LG_STATUS_QUERY|Query the status of all LOGE functions: temperatures, relays, version|
| 0x03|VN_ALERT|An alert message from Venus. The data contains where the alert originates|
|0x04|VN_QUERY|Query the status of Venus functions|
|0x05|LG_STATUS_REPLY|Status reply from LOGE. This will be encapsulated in Venus data when forwarded.|
|0x06|VN_STATUS_REPLY|Status reply of Venus data. |
|0x07|LG_RQTEMP_HISTORY|Request temperature history from LOGE. |
|0x08|VN_RQTEMP_HISTORY|Request temperature history from Venus. |




==== Typical scenarios ====
1. BB Venus periodically polls LOGE, LOGE responds with status
  * VENUS: (presynch) 0x7f, 0xfe, (dst address)0x81, (src address)0x80, (opcode) 0x02, (length) 0x06, crc lo, crc hi
  * LOGE: (presynch) 0x7f, 0xfe, (dst address)0x80, (src address)0x81, (opcode) 0x02, (length) 0x06, crc lo, crc hi
2. Downing Venus polls LOGE. BB Venus receives poll, sends to LOGE, LOGE responds, Venus sends it out the gateway to the TNC
  * VENUS downing: (presynch) 0x7f, 0xfe, (dst address)0x81, (src address)0x00, (opcode) 0x02, (length) 0x06, crc lo, crc hi
  * VENUS BB: (presynch) 0x7f, 0xfe, (dst address)0x81, (src address)0x00, (opcode) 0x02, (length) 0xxx, 
  * LOGE BB: (presynch) 0x7f, 0xfe, (dst address)0x00, (src address)0x81, (opcode) 0x05, (length) 0xxx, crc lo, crc hi
  * VENUS BB: (presynch) 0x7f, 0xfe, (dst address)0x00, (src address)0x80, (opcode) 0x07, (length) 0xxx,