Although it is possible to create a program that consists of a simple series of networks, SYSWIN encourages you to break down a program into groups of networks, which form functional blocks.
The concept programming in block is designed not only to make it easier for you to work through a program, by splitting it into manageable chunks, but also to maintain the program after it has been in use for a while. Programming in blocks also eases the process of creating library modules that can be incorporated into future programs.
SYSWIN encourages the creation of groups of networks within blocks, again promoting the concept of working in a structured manner, as shown in this example:
With CV series PLCs, interrupt routines are held in separate blocks, and main blocks are sequential and joined together. For both C and CV series, the last block in main program must contain the END instruction, as normal.
Normally you would not be connected to the PLC when preparing the main structure of a program. After programming you would check the program carefully before connecting and downloading it to the PLC. Checking of program syntax and validity of function is done by SYSWIN at various times as a protective mechanism, but any logical checking that you do speed up the debugging process.