Project Components and How They Work (GS 2.4)
In STEP 7-Micro/WIN 32, the project provides you with a means of associating your program with all the information that is needed in order for you to communicate with a PLC and download the given program to that particular PLC.
A project is composed of these fundamental components:
Program Block The program block is composed of executable code and comments. The executable code consists of a main program (OB1) and any subroutines or interrupt routines. The code is compiled and downloaded to the PLC; the program comments are not.
Data Block The data block is composed of data (initial memory values; constant values) and comments. The data is compiled and downloaded to the PLC; the comments are not.
System Block The system block consists of configuration information such as communications parameters, retentive data ranges, analog and digital input filters, output values for a STOP transition, and password information. The system block information is downloaded to the PLC.
Symbol Table The symbol table is a means for allowing the programmer to use symbolic addressing. Symbols are sometimes more convenient for the programmer, and make program logic easier to follow. The compiled program that is downloaded to the PLC converts all symbols to absolute addresses. Symbol table information is not downloaded to the PLC.
Status Chart Status charts allow you to observe how process values are affected as your program executes. Status charts are not downloaded to the PLC; they are simply a means of monitoring PLC (or simulated PLC) activity.
Cross Reference The Cross Reference window lets you examine tables that list where operands are used in your program, and also which areas of memory have already been assigned (Bit Usage and Byte Usage). During a program edit in RUN mode, you can also examine the edge numbers (EU, ED) that are currently in use by your program. Cross reference and usage information is not downloaded to the PLC.
ˇYou cannot upload status chart, cross reference, or symbol table information from a PLC unless you download first.
ˇThe modifications you make to a project in STEP 7-Micro/WIN 32 have no impact on your process until you download them to the PLC.