t allows the CHOICE construct (similar to a C union). In addition, several protocol standards use ASN.1 to describe data. 8.1.4 Adding buttons to the Simulator 8.1.4.1 The three Simulator definition files As shown in Figure 8.9, the buttons and menus present in the Simulator are defined in the file def.btns. The content of the Command Window is defined in def.cmds, and the variables to display in a watch are defined in def. vars. The names and location of each definition file can be changed in the Preferences Manager (from the Organizer). The Simulator loads the first of each file, searching in the following order: the current directory, the user's home directory and the installation directory. Other Simulator Features 271 Organizer v76.sdt File Edit View Generate Tools Help h my_c.h Move Up nw my_c.h ctypes SDL System Structure rw v76.sun V76_DLC nw v76_dlc.sbt dispatch rw dispatch.spr nw dlc.spr V76test v76test.ssy DLCa: V76_DLC DLCb: V76_DLC dataLink nw datalink.sbk AtoB toPeer BtoA toPeer toPeer topeer.spt Move the selected document up Figure 8.8 The Organizer after adding ctypes Buttons & menus def.btns Command window def.cmds Simulator Variables in watch def.vars Figure 8.9 The three Simulator definition files 8.1.4.2 Adding four buttons to the Simulator We are going to add two groups Service User A and Service User B to the Simulator. Then we will add four buttons to these groups, as shown in Figure 8.10. A. In the Simulator, select Buttons > Add Group, enter Service User A and press Apply, enter Service User B and press OK. B. Press the button Group in Service User A and select Add. C. Type EstabReq(0) in the field Label, and Output-To L_EstabReq(0) <Block DLCa: dispatch in the field Definition. Press Apply. D. Enter DataReq(0,5) in the field Label, and Output-To L_DataReq (0,5)<<BlockDLCa>> dispatch in the field Definition. Press Apply. E. Enter Release(0) in the field Label, and Output-To L_ReleaseReq(0) <<Block DLCa>> dispatch in the field Definition. Press OK. 272 Validation of Communications Systems 