JRBusTCP is a proprietary binary communication protocol designed for efficient, deterministic data exchange between JRobo / JRoboPLC instances and client applications. The protocol operates over TCP/IP and is optimized for:

• High-frequency data exchange
• Minimal bandwidth usage
• Deterministic behavior suitable for automation and PLC-like systems
• Explicit control over data serialization and transport

The protocol follows a request/response model with client-initiated communication. All messages are framed, version-agnostic at transport level, and protected by CRC32 checksums.

Maximum supported message size is 16384 bytes.

—

• Transport protocol: TCP
• Connection model: persistent TCP connection
• Byte order: Big Endian (network byte order)
• Encoding for strings: UTF-8

JRBusTCP does not define connection establishment beyond TCP. Session state (authentication, tag list, update state) is maintained per TCP connection.

—

+--------+--------+----------------------------+--------+
| size   | header | payload                    | crc    |
| 2 B    | 2 B    | (size - 4 - 4 bytes)       | 4 B    |
+--------+--------+----------------------------+--------+

Where payload has the following structure:

+---------+------+---------------------------+
| reqId   | cmd  | body                      |
| 4 B     | 1 B  | variable length           |
+---------+------+---------------------------+

• size (2 bytes): Total message size in bytes, from `header` through `crc` inclusive
• header (2 bytes): Constant magic value `0xABCD`
• reqId (4 bytes): Request identifier (int32, signed). Generated by client
• cmd (1 byte): Command code
• body (variable): Command-specific payload
• crc (4 bytes): CRC32 calculated over `[reqId..body]`

• Generated by the client
• Initial value SHOULD be random
• Incremented by 1 for each subsequent request
• Server MUST return the same `reqId` value unchanged
• Client MUST verify response `reqId` matches request

Server does not validate or interpret `reqId`.

—

Response commands are formed by setting the highest bit (`cmd | 0x80`).

—

Initializes tag list and session parameters.

cmd        : 0x01
flen       : 1 byte
filter     : flen bytes (UTF-8 regex)
clen       : 1 byte
client     : clen bytes (UTF-8)
flags      : 2 bytes 

• b0: Client supports tag descriptions
• b1: Client supports tag status in READ
• b2: Exclude tags with `external` flag
• b3: Include tags with `hidden` flag

cmd        : 0x81
listsize   : 3 bytes (uint24) 

`listsize` indicates total number of tags selected.

—

Retrieves tag metadata in chunks.

cmd   : 0x02
index : 3 bytes (uint24) 

cmd      : 0x82
index    : 3 bytes
quantity : 3 bytes
next     : 3 bytes
[tag entries] 

type    : 1 byte
nlen    : 1 byte
tagname : nlen bytes (UTF-8)
dlen    : 1 byte
descr   : dlen bytes (UTF-8) 

—

Checks for tag value changes.

cmd : 0x03 

cmd        : 0x83
quantity   : 3 bytes
next       : 3 bytes
liststate  : 1 byte 

• 0x00: tag list unchanged
• 0xFF: tag list changed; client MUST re-run INIT + LIST

—

Reads tag values.

cmd   : 0x04
index : 3 bytes 

cmd      : 0x84
index    : 3 bytes
quantity : 3 bytes
next     : 3 bytes
[data blocks] 

• 0xFE: Next tag index, uint16
• 0xFF: Next tag index, uint24

• 0xF0: false / zero
• 0xF1: true / one
• 0xF2: 1-byte integer
• 0xF3: 2-byte integer

• 0xF8: int32 (4 bytes)
• 0xF9: int64 (8 bytes)
• 0xFA: double (8 bytes)
• 0xFB: string (2-byte length + UTF-8 bytes)

Status bit: b4 of first value byte (if INIT.flags.b1 = 1)

• 1 = Good
• 0 = Bad

—

Writes tag values.

cmd      : 0x05
index    : 3 bytes
quantity : 3 bytes
[data blocks] 

cmd : 0x85 

—

Returns CRC32 checksum of all tag values after last UPDATE.

cmd : 0x06 

cmd : 0x86
crc : 4 bytes 

—

request:
cmd      : 0x07
klen     : 2 bytes
keyname  : klen bytes

response:
cmd      : 0x87
status   : 1 byte
nlen     : 2 bytes
nonce    : nlen bytes 

Status:

• 0x00 OK
• 0x01 FAILED
• 0x02 DISABLED

request:
cmd      : 0x08
nlen     : 2 bytes
nonce    : nlen bytes

response:
cmd      : 0x88
status   : 1 byte 

Status:

• 0x00 ACCEPTED
• 0xFF DENIED

—

• 0xFE: UNAUTHENTICATED
• 0xFF: UNKNOWN

—

1. TCP connect
2. AUTH_INIT / AUTH_SUBMIT (optional)
3. INIT
4. LIST (paged)
5. UPDATE
6. READ / WRITE
7. CRC (optional)
8. TCP disconnect

—

• Protocol favors deterministic binary layout
• Compact encodings reduce bandwidth
• Explicit pagination avoids oversized frames
• reqId enables async request matching

—

This document defines JRBusTCP Protocol v1. Any incompatible changes MUST increment protocol version and be negotiated out-of-band.

—

Client                          Server
|                                 |
|--- TCP CONNECT ---------------->|
|                                 |
|--- INIT ----------------------->|
|<-- INIT RESPONSE (listsize) ----|
|                                 |
|--- LIST (index=0) ------------->|
|<-- LIST (chunk 1) --------------|
|--- LIST (next) ---------------->|
|<-- LIST (last chunk) -----------|
|                                 |
|--- UPDATE --------------------->|
|<-- UPDATE (quantity,next) ------|
|                                 |
|--- READ (index=first changed) ->|
|<-- READ (values) ---------------|
|                                 |
|--- UPDATE / READ (loop) --------|
|                                 | 

+---------+------+---------+-----------+-----------+----------------+
| reqId   | cmd  | index   | quantity  | next      | data blocks    |
| 4 B     | 1 B  | 3 B     | 3 B       | 3 B       | variable       |
+---------+------+---------+-----------+-----------+----------------+ 

+---------+------+---------+-----------+----------------+
| reqId   | cmd  | index   | quantity  | data blocks    |
| 4 B     | 1 B  | 3 B     | 3 B       | variable       |
+---------+------+---------+-----------+----------------+ 

—

• Determinism: binary layouts provide predictable parsing cost
• Zero allocations: no intermediate object trees required
• Bandwidth efficiency: compact numeric encodings outperform JSON
• Schema stability: no dependency on external IDL or runtime reflection

• Guaranteed delivery and ordering
• Built-in congestion control
• Simplified client/server implementations
• NAT/firewall friendly

—

00 1A AB CD 00 00 00 01 01
05 2E 2A 00 06 4A 52 6F 62 6F
00 03
A1 B2 C3 D4 

00 14 AB CD 00 00 00 05 84
00 00 01 00 00 01 00 00 00
F8 00 00 00 2A
DE AD BE EF 

—

• Typical RTT dominated by TCP latency
• Binary parsing cost negligible
• Suitable for polling rates up to several kHz on LAN

• READ/WRITE support bulk operations
• Clients SHOULD batch contiguous tag indices
• Server SHOULD maximize quantity per response until size limit reached

• Poll UPDATE at fixed interval (e.g., 10–100 ms)
• Issue READ only when quantity > 0
• Use CRC command to validate full state synchronization when needed