Hardware Protocol Specification: 9-bit UART multidrop addressing

Version: generic (common 8051/PIC UART mode)
Physical Layer: 9600 bps, 9N1.0
Framing: binary
Integrity Algorithm: sum8

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Description

RS-485 multidrop scheme common on small microcontroller UARTs: a 9th data bit (not parity) flags whether a byte is an ADDRESS (bit=1) or DATA (bit=0), so slaves can filter in hardware without the CPU inspecting every byte. dataBits=9 was already a valid enum value but never actually exercised until now.

Command Catalog & Message Signatures

Category: GENERAL

SlaveMessage (Command ID: 0x00) - The 9th bit is now representable directly via each field's ninthBitSet.

Parameter	Type	Unit	Range / Constraints	Options
address	uint8	-	-	-
data	bytes	-	-	-
checksum	uint8	-	-	-

Formal AsyncAPI 2.6.0 Specification

asyncapi: 2.6.0
info:
  title: 9-bit UART multidrop addressing
  version: generic (common 8051/PIC UART mode)
  description: 'RS-485 multidrop scheme common on small microcontroller UARTs: a 9th
    data bit (not parity) flags whether a byte is an ADDRESS (bit=1) or DATA (bit=0),
    so slaves can filter in hardware without the CPU inspecting every byte. dataBits=9
    was already a valid enum value but never actually exercised until now.'
servers:
  serial_link:
    url: serial://tty/9600
    protocol: serial
    description: Physical UART Transport (9600 bps, 9N1.0)
    bindings:
      serial:
        baudRate: 9600
        dataBits: 9
        parity: none
        stopBits: 1.0
        framingType: binary
        integrity: sum8
channels:
  omniuart/cmd/SlaveMessage:
    publish:
      summary: 'Send command SlaveMessage (ID: 0x00)'
      description: The 9th bit is now representable directly via each field's ninthBitSet.
      message:
        name: SlaveMessage_Message
        title: SlaveMessage Command
        payload:
          $ref: '#/components/schemas/SlaveMessage_Request'
components:
  messages: {}
  schemas:
    SlaveMessage_Request:
      type: object
      properties:
        command_id:
          type: integer
          const: 0
          description: Opcode ID for SlaveMessage
        address:
          type: integer
        data:
          type: string
          contentEncoding: base64
        checksum:
          type: integer
      description: The 9th bit is now representable directly via each field's ninthBitSet.