File syn_modbus_tcp.h¶

FileList > proto > syn_modbus_tcp.h

Modbus TCP ADU (MBAP) framing layer. More...

#include "../common/syn_defs.h"
#include "syn_modbus.h"
#include "syn_modbus_master.h"
#include <stdbool.h>
#include <stddef.h>
#include <stdint.h>

Classes¶

Type	Name
struct	SYN_MBAP_Header Modbus TCP MBAP Header structure.

Public Functions¶

Type	Name
bool	syn_mbap_decode_header (const uint8_t * buf, SYN_MBAP_Header * hdr) Decode an MBAP header from a byte buffer.
void	syn_mbap_encode_header (const SYN_MBAP_Header * hdr, uint8_t * buf) Encode an MBAP header into a byte buffer.
SYN_Status	syn_modbus_tcp_build_client_adu (uint16_t transaction_id, uint8_t unit_id, const uint8_t * pdu, uint16_t pdu_len, uint8_t * req_adu, uint16_t req_max, uint16_t * req_len) Build a Modbus TCP Master request ADU.
bool	syn_modbus_tcp_process_slave (SYN_Modbus * mb, const uint8_t * req_adu, uint16_t req_len, uint8_t * resp_adu, uint16_t resp_max, uint16_t * resp_len) Process an incoming Modbus TCP ADU frame on a Modbus Slave instance.

Macros¶

Type	Name
define	SYN_MBAP_HEADER_LEN `7`
define	SYN_MB_TCP_MAX_ADU `260`

Detailed Description¶

Implements Modbus TCP MBAP (Modbus Application Protocol) header framing over TCP transport sockets (syn_transport_tcp).

MBAP Header Structure (7 bytes): * Transaction ID (2 bytes, big-endian) * Protocol ID (2 bytes, big-endian, 0x0000 = Modbus) * Length (2 bytes, big-endian, length of remaining bytes) * Unit ID (1 byte, target slave/server address)

Followed by standard Modbus PDU (Function Code + Data). Note that Modbus TCP does NOT include RTU CRC-16.

Public Functions Documentation¶

function syn_mbap_decode_header¶

Decode an MBAP header from a byte buffer.

bool syn_mbap_decode_header (
    const uint8_t * buf,
    SYN_MBAP_Header * hdr
)

Parameters:

buf Input byte buffer (must be at least 7 bytes).
hdr Pointer to destination MBAP header structure.

Returns:

true if valid Modbus protocol ID (0x0000).

function syn_mbap_encode_header¶

Encode an MBAP header into a byte buffer.

void syn_mbap_encode_header (
    const SYN_MBAP_Header * hdr,
    uint8_t * buf
)

Parameters:

hdr Pointer to MBAP header structure.
buf Output byte buffer (must be at least 7 bytes).

function syn_modbus_tcp_build_client_adu¶

Build a Modbus TCP Master request ADU.

SYN_Status syn_modbus_tcp_build_client_adu (
    uint16_t transaction_id,
    uint8_t unit_id,
    const uint8_t * pdu,
    uint16_t pdu_len,
    uint8_t * req_adu,
    uint16_t req_max,
    uint16_t * req_len
)

Parameters:

transaction_id Transaction sequence number.
unit_id Target Unit ID (slave address).
pdu Raw PDU bytes (Function Code + Data).
pdu_len PDU length in bytes.
req_adu Output buffer for complete Modbus TCP ADU.
req_max Output buffer capacity.
req_len Out: Total ADU length (7 + pdu_len).

Returns:

SYN_OK on success, SYN_NO_MEMORY if buffer too small.

function syn_modbus_tcp_process_slave¶

Process an incoming Modbus TCP ADU frame on a Modbus Slave instance.

bool syn_modbus_tcp_process_slave (
    SYN_Modbus * mb,
    const uint8_t * req_adu,
    uint16_t req_len,
    uint8_t * resp_adu,
    uint16_t resp_max,
    uint16_t * resp_len
)

Takes a full Modbus TCP ADU (MBAP header + PDU), processes the PDU using the Modbus slave engine, and builds the corresponding Modbus TCP response ADU.

Parameters:

mb Modbus RTU/PDU slave instance.
req_adu Input Modbus TCP request ADU buffer.
req_len Length of request ADU in bytes.
resp_adu Output Modbus TCP response ADU buffer.
resp_max Capacity of response ADU buffer.
resp_len Out: Length of generated response ADU in bytes.

Returns:

true if response ADU generated, false if no response (or invalid ADU).

Macro Definition Documentation¶

define SYN_MBAP_HEADER_LEN¶

#define SYN_MBAP_HEADER_LEN `7`

MBAP header length in bytes

define SYN_MB_TCP_MAX_ADU¶

#define SYN_MB_TCP_MAX_ADU `260`

Max Modbus TCP ADU (7 MBAP + 253 PDU)

The documentation for this class was generated from the following file src/syntropic/proto/syn_modbus_tcp.h