Architecture

flowchart LR
  A["Host application<br/>C, C++, Python, or msc"]
  B["Ethernet submaster<br/>UDP port 1177"]
  C["RS-485 segment<br/>9-bit addressing"]
  D["Node 0…65535"]
  E["Node variables<br/>measurements and settings"]
  A -->|"MSCB library API"| B
  B -->|"MSCB command payload"| C
  C --> D
  D --> E

Host and submaster

The host library builds MSCB commands, manages retries, and sends them to a submaster. The Ethernet implementation wraps each RS-485 transaction in a small UDP header containing payload size, sequence number, flags, and protocol version. The submaster applies the requested ninth-bit and timing behavior to the physical bus and returns the node response.

Addressing

Every node has a 16-bit node address and a 16-bit group address. A master can select:

• one node, for commands that may return a response;
• a group, for simultaneous no-acknowledge writes; or
• all nodes by broadcast.

Address 0xFFFF is the factory/unconfigured node address. New nodes can be found there and assigned a permanent address. Address commands are transmitted with serial bit 9 set; ordinary commands have bit 9 clear.

Self-documenting variables

A node exposes as many as 256 variables. Each variable has an index, width, name, unit, SI prefix, status, and flags describing such properties as floating point, signedness, hidden configuration, or remote routing. Clients query this metadata with MCMD_GET_INFO, then encode values appropriately.

Variables live in node RAM. MCMD_FLASH asks the node to copy its current values and configuration to non-volatile storage. Because EEPROM has limited write endurance, flashing should be deliberate rather than automatic after every write.

Master/slave behavior

The ordinary protocol is master/slave: only an addressed node responds. Group and broadcast requests must not provoke multiple responses, because that would cause an RS-485 collision. MCMD_TOKEN is reserved for a token-ring arrangement when multiple masters share a bus.

Data paths

Operation	Command family	Typical use
Discover	PING8, PING16	Test whether an address responds
Describe	GET_INFO	Read node and variable metadata
Read	READ, READ_RANGE	Acquire one or several variables
Write	WRITE_NA, WRITE_ACK, WRITE_RANGE	Set variables
Persist	FLASH	Copy current configuration to EEPROM/flash
Memory transfer	READ_MEM, WRITE_MEM	Firmware and block access
Diagnostics	ECHO, GET_UPTIME, LOG	Verify and inspect operation