PLC programming should follow basic principles.
1) external input contacts, output relays, internal relays, timers, counters and other devices can be repeatedly used, without using complicated structure of the program to reduce the use of contacts.2) Each line of the ladder left the bus started, the coil connected to the far right, the right contacts can not be placed coils
3) coil can not be directly connected to the left bus bar. If desired, you can connect via a normally closed contact does not use internal relays or special internal relay R9010 (often 0N) normally open contacts,
4) the same number of coils known as dual-coil output twice in one program. Double coil output prone to misuse, should be avoided coil reused.5) Ladder program must comply with the principles of the order of execution, that is from left to right, top to bottom implementation does not comply with the order of execution of the circuit can not be programmed directly, such as the bridge circuit shown in Figure 4-22 can not be programmed directly .
6) contacts in series and parallel contacts in the ladder use is unlimited, unlimited use
7) two or more coils can be connected in parallel output,
PLC ONE 