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Using Socket Services by Manipulating Dedicated Control Bits Section 6-7
R: Read by user for results at completion
---: Not used.
6-7-4 Parameters
■ Socket Option
For the TCP OPEN REQUEST (ACTIVE or PASSIVE) command, specifies
whether or not the keep-alive function is to be used. When the keep-alive
function is used, bit 8 is ON (set to 1).
■ UDP/TCP Socket No.
Specify the number of the UDP or TCP socket to open.
■ Local UDP/TCP Port No.
Specify the number of the UDP or TCP port for the socket to use for
communications.
• Do not specify the port being used as the FINS UDP port (default: 9600)
in an open request for a UDP socket.
• Do not specify FTP server TCP port numbers 20 and 21 in an open
request for a TCP port.
• Do not specify mail communications TCP port number 25.
• As a rule, use port numbers 1,024 and higher.
If port number 0 is specified when for an active TCP open, the TCP port
number will be automatically allocated and the number of the port that was
opened will be stored in the local UDP/TCP port number in the Socket Service
Parameter Area (i.e., the actual port number will be overwritten on the value of
0 set by the user).
■ Remote IP Address
Specify the IP address of the remote device.
• Offset +2 in the Socket Service Parameter Area contains the upper bytes
of the Remote IP Address, and offset +3 contains the lower bytes.
Example: The contents of offsets +2 and +3 would be as shown below
when the Remote IP Address is 196.36.32.55 (C4.24.20.37 hexadeci-
mal).
+2:C424
+3: 2037
• This parameter is not used when making a receive request for a UDP
socket. The remote IP address will be stored with the response data and
will be written as the Remote IP Address in the Socket Service Parameter
Area.
• When opening a passive TCP socket, the combination of the remote IP
address and the remote TCP port number can be used to affect process-
ing as shown in the following table.
Remote IP
Address
Remote TCP
Port No.
Processing
0 0 All connection requests accepted.
0 Not 0 Connection requests accepted only for the same
port number.
Not 0 0 Connection requests accepted only for the same IP
address.
Not 0 Not 0 Connection requests accepted only for the same
port number and IP address.