NAME

modbus_new_tcp_pi - create a libmodbus context for TCP Protocol Independent

SYNOPSIS

modbus_t *modbus_new_tcp_pi(const char *node, const char *service);

DESCRIPTION

The modbus_new_tcp_pi() function shall allocate and initialize a modbus_t structure to communicate with a Modbus TCP IPv4 or IPv6 server.

The node argument specifies the host name or IP address of the host to connect to, eg. "192.168.0.5" , "::1" or "server.com". A NULL value can be used to listen any addresses in server mode.

The service argument is the service name/port number to connect to. To use the default Modbus port use the string "502". On many Unix systems, it’s convenient to use a port number greater than or equal to 1024 because it’s not necessary to have administrator privileges.

RETURN VALUE

The function shall return a pointer to a modbus_t structure if successful. Otherwise it shall return NULL and set errno to one of the values defined below.

ERRORS

EINVAL

ENOMEM

EXAMPLE

modbus_t *ctx;
ctx = modbus_new_tcp_pi("::1", "1502");
if (ctx == NULL) {


    fprintf(stderr, "Unable to allocate libmodbus context\n");


    return -1;
}
if (modbus_connect(ctx) == -1) {


    fprintf(stderr, "Connection failed: %s\n", modbus_strerror(errno));


    modbus_free(ctx);


    return -1;
}

SEE ALSO

modbus_new_tcp(3) modbus_tcp_pi_listen(3) modbus_free(3)

AUTHORS

The libmodbus documentation was written by Stéphane Raimbault <stephane.raimbault@gmail.com>