FCT_SELECT: Multiplexes Requests Over Sockets

Function Description

The FCT_SELECT function is used to multiplex I/O requests among multiple sockets. It indicates which sockets have events to process using an array of integers.

For ETY 5103 firmware revision 3.3 or lower:

The socket descriptors are assigned a socket number from 1 to 32:
- Numbers from 1 to 16 are assigned to sockets created by the Socket function. They are client sockets.
- Numbers from 17 to 32 are assigned to sockets created by the Accept function. They are server sockets.
The array of the MASK (Socket_Activity) is for diagnosing the status of the listening (server) and connected (client) sockets.
- Server Perspective: Any word of the array uses available bits of the array to correspond to the listening socket in the initial step. The Accept function outputs a different socket number to locate its associated bit in the second word of the array, which reports the status of the server connection.
- Client Perspective: The first word of the array reports the status of the client connection.

For ETY 5103 firmware greater than revision 3.3:

You may have up to 64 sockets that can be used as listening (server) sockets or connected (client) sockets. In a server application, at least 1 socket must be a listening socket. There are no other hard boundaries regarding listening versus connected sockets.
To determine the listening sockets, see the socket number provided as output by the Socket function.
To determine the connected sockets, see the socket number provided as output by the Accept function.
The array of the MASK (Socket_Activity) is for diagnosing the status of the listening and connected sockets, which are now combined into a 2- or 4-word array (see note below). You must use the output of the Socket or Accept function to locate the corresponding bit in the array. See the Socket_Activity in the Description of Parameters table.

NOTE: For versions higher than 3.3, a length parameter is required in the Management_Param structure.

The length field is not used when the high byte of the INTE parameter is set to 00. You should set the length to 8 when the high byte of the INTE parameter is set to 01. A setting of 8 allows you to see the data associated with all 64 connections. If you set the value lower, say to 4, you will see only the data associated with the first 32 connections.

The additional parameters and may be configured.

Representation in FBD

Representation in LD

Representation in IL

LD Module_Number

FCT_SELECT Mask_Index, Gest_Index, Management_Param, Socket_Activity

Representation in ST

FCT_SELECT(Module_Number, Mask_Index, Gest_Index, Management_Param, Socket_Activity);

Description of Parameters

The following table describes the input parameters:

Parameter	Type	Comment
Module_Number	INT	Slot number of network module in rack 0. Low byte is the slot number of network module in rack 0. High byte can be used to extend the number of sockets. 00: Provided for full backward compatibility with applications created on firmware version 3.3 or earlier. 01: Up to 64 sockets can be used (firmware version must be higher than 3.3).
Mask_Index	INT	Index of first word in the Socket_Activity array
Gest_Index	INT	Index of first word in Management_Param array

The following table describes the input/output parameters:

Parameter	Type	Comment
Management_Param	ARRAY [0... 3] OF INT	Function management array For this function, the operation report always returns the value 16#00 indicating that no error has occurred.

The following table describes the output parameters:

Parameter	Type	Comment
Socket_Activity	ARRAY [0... 1] OF INT - or - ARRAY [0... 3] OF INT (Refer to the note in the Function Description topic.)	Status of each socket. Each bit set to 1 indicates an event on the socket which corresponds to this bit. For example: For version 3.3 or earlier: If bit 5 of the first word has the value 1, socket 6 will be read by the FCT_ACCEPT function. If bit 3 of the second word has the value 1, socket 20 will be read by the FCT_RECEIVE function. For versions later than 3.3: If a bit is set to 1 on a listening socket, a server is ready to accept this connection. If a bit is set to 1 on a connected socket, data is ready to be sent or communication has been interrupted. Client Perspective: Once you have a client connection, the corresponding bit for the connection (socket number) is set to 1 in the array. Example: Socket 33 will be found in the third word, first bit (bit 0). Server Perspective: The listening function opens a socket. This socket number has a corresponding bit set to 1 in the array. Example: Socket 3 will be found in the first word, third bit (bit 2). Then, the Accept function will return a different socket number, and this socket number will have a corresponding bit set to 1 in the array. NOTE: The listening function socket number bit will remain set to 1 until the socket is closed.