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
-
The node string is empty or has been truncated. The service string is empty or has been truncated.
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; }
AUTHORS
The libmodbus documentation was written by Stéphane Raimbault <stephane.raimbault@gmail.com>