# modbus_new_tcp_pi(3) Manual Page

## 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.

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 modbus_new_tcp_pi() 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;
    }

## SEE ALSO

modbus_new_tcp(3) modbus_new_rtu(3) modbus_free(3)

## AUTHORS

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