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<concept xml:lang="en" id="GUID-D99D9DA3-AB82-5513-85C3-FFF254CB9B0B"><title>What are Serial Ports</title><shortdesc>The term <i>Serial Port</i> has different meanings at the different levels within the Serial Communications Server. These differences are caused by each level defining classes to represent a serial port. </shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody><p>At the client application level, the serial port is represented by the <xref href="GUID-3B4E8ED5-72F7-3E51-B188-3C1045526DDF.dita"><apiname>RComm</apiname></xref> API. The <codeph>RComm</codeph> API is used to open a particular serial port. The <codeph>RComm</codeph> API is used to read, write, configure, set break conditions, and get port state information. Each serial port is named by a text string to describe the protocol for the port and a number. The format is: </p> <codeblock id="GUID-EEE22754-3CA9-57C5-A67D-0A690A3D2A25" xml:space="preserve">[text-string]::[0-255]</codeblock> <p>The protocol name and the range of possible numbers come from the CSY. The number zero (0) is used for the first port. For example, the port <codeph>COMM::0</codeph> is the first port of the CSY named <codeph>COMM</codeph>. The <codeph>COMM</codeph> CSY is used to provide the RS232 serial protocol. Another example is the port <codeph>ACM::0</codeph> which is the first port of the USB CSY. </p> <p> <i>NOTE</i>: The filename for the CSY may be different to the string used to open ports with the same CSY. To load a CSY the filename must be provided. For example, to load the RS232 CSY, the filename <filepath>ecuart.csy</filepath> must be provided, while to open RS232 ports the name <codeph>COMM</codeph> must be used. </p> <p>At the Serial Communications Server level, a serial port is represented by two classes in the CSY. These two classes are <xref href="GUID-D8C11F99-7452-35BB-B53E-440968D4C1A3.dita"><apiname>CSerial</apiname></xref> and <xref href="GUID-5CEF7907-E485-3626-8587-53CAC2A06544.dita"><apiname>CPort</apiname></xref>. These classes are not available to client applications. To create a port, the server gives the <codeph>CSerial</codeph> class a number for the port number, which results in a <codeph>CPort</codeph> class being created for that number. The instance of the <codeph>CPort</codeph> class then represents the port. </p> </conbody></concept>