I apologize for the inconvenience, but i did not found the "answer"...
I'm developing (trying) an Eclipse plugin to integrate JCDK in Eclipse (of course :-) ) as University Final Project.
The project has several goals, in which one of them is to add debugging support to the javacard applications. This is one great idea, but i find lack of information regarding one debugger tool in JCDK.
I read in the documentation, that version 3.0.2 connected and 3.0.4 classic has one "debugproxy" which i still could not understand. But regarding the version 2.x.x i could not found any concrete information. in the site http://java.sun.com/javacard/overview.jsp mention:
"... The toolkit is a Java Card simulator and debugger that has been designed for integration into third-party integrated development environments ...", however i couldn't found any article explaining how does it work.
I believe that the protocol is java debug wire protocol (or java card debug wire protocol). The JCWDE runs your applet as native Java code so a standard Java debugger should also work. I am not sure that CREF has debugger support built in.