Sheetal,
You can set the termination character by setting the VI_ATTR_TERMCHAR attribute. You must also set the VI_ATTR_TERMCHAR_EN attribute to true in order to enable read termination. Both attributes are set using the viSetAttribute function. If you expect the same termination character for the entire session, you can just set the termchar attribute once, otherwise you must make sure it is set appropriately before each viRead call.
Note also that ComRdByte removes both the carriage return and line feed if your termination character is a carriage return or line feed and both are encountered. I do not believe this is the case for viRead.
Hope this helps.
Mert A.
National Instruments