CAAPE User's Manual - ALSTOM Signaling Inc.

General Rules and Techniques5.2.2. Symbol Declaration and UsageDeclaring a symbol reserves a memory location for it within the application. Thishappens when:• The symbol is used as a hardware input or a bit in an incoming message• The symbol is named as an internal variable in application logic• The symbol is automatically made the result of a CAA-generated equationIn most cases, the same symbol name cannot be declared twice in the sameapplication, i.e. in the I/O, messages or logic for a single processor board. However, thename might be used many times as output or equation variables in the sameapplication.For example, if VRDFRNT-DI is a direct input in a VPI application it cannot be used asanother hardware input, as a Vital serial or CSEX-to-VPI message bit, or as a CurrentResult or Self-Latched logic variable. However, it can be used as many times as neededas bits in outgoing Vital serial messages or as a parameter variable (not a result) in Vitallogic equations.NOTEThe same symbol name can be declared in different applications in thesame system. From the above example, VRDFRNT-DI could be sent to aCSEX board in a VPI-to-CSEX message and, on the CSEX side, declaredas a VPI-to-CSEX message bit. Since the VPI and CSEX applications runon separate boards, the same name can be used in each.P2512A, Rev. Oct/09 5–2 Alstom Signaling Inc.