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10-1 About Socket Services
This subsection provides an outline of PC Card Unit socket services.
10-1-1 Sockets
A socket is an interface which allows a user program to directly use TCP (Trans-
mission Control Protocol) and UDP (User Datagram Program).
Socket services allow arbitrary data to be sent to and from other nodes, thereby
enabling communications in any protocol with FA computer other than OMRON
PCs, with UNIX workstations, and so on.
Socket services are supplied for most host computers (or some personal com-
puters) as a C-language interface library. This interface library allows user pro-
grams to communicate using TCP and UDP.
The socket interface is supported for UNIX workstations in the form of system
calls.
Socket services are achieved for C200HX/HG/HE PCs by sending FINS com-
mands from the user program to a PC Card Unit. Refer to Section 9 FINS Com-
mands, 10-2 Using Socket Services, 10-3 Sample Programs for TCP and UDP
Communications, and Section 11 FINS Commands and Responses.
10-1-2 Socket Operation
A socket operates as shown in the following diagram when communicating
between an FA computer and a PC Card Unit. Data from the computer or
C200HX/HG/HE PC passes through the socket and is communicated using the
TCP or UDP protocol.
Program
System
call
I
P
TCP
UDP
Socket
TCP
UDP
TCP
UDP
Socket
I
P
Host computer
FINS
command
FINS
response
CPU
PC Card Unit
C200HX/HG/HE
10-1-3 Differences between TCP and UDP
There are differences in the socket services between TCP and UDP.
TCP Communications
The following procedure is followed each time data is transmitted to ensure that
the data arrives properly at the destination node:
1, 2, 3...
1. The destination node returns ACK when data is received normally.
2. The local node sends the next data after it receives ACK, or it resends the
same data if ACK is not returned within the specified time.
Local node
Transmitted data
ACK
Re-transmitted data
Destination node
About Socket Services
Section 10-1
Summary of Contents for SYSMAC C200HW-PCS01-EV1
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