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Showing results for tags 'constant'.
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Hello. I'm having difficulties of how to write REAL constant in ST. For example (Gap1 is defined as REAL): Gap1:= UDINT_TO_REAL(P_Cycle_Time_Value) / +1000.0; RETURNS ERROR ERROR: Conversion cannot convert from Integer Literal to REAL I have also tried 1000.0 If I use: Gap1:= UDINT_TO_REAL(P_Cycle_Time_Value) / INT_TO_REAL(1000); COMPILES OK My question.. How do I write REAL constant in Structure text? I don't want to use INT_TO_REAL anytime I want to do calculations with constants.. Thanks. BR.
Hello all, I'm quite new to PLC programming, but having learnt digital electronics and programming in PASCAL and C in the 90s, I'm trying to implement a Finite State Machine within an FX5u PLC to control an industrial automation. If it was something for myself that wouldn't require flexibility, I hard-wired it using logic gates, a counter, and latches for inputs and outputs, done several Karnaugh diagrams to simplify the circuit, and so on. If it did require flexibility and it was for a hobby, I'd probably gone for an Arduino or a simple program running in a raspberry pi. However, and since it's for work, I have to use the tools that my fellow co-workers use. Now, in my company they use mostly Mitsubishi PLCs, but they tend to program everything in ladder and using huge, complex programs which are a pain to trace and debug, with a very slow execution time. They also tend to program in iterative steps, but they rely on a clean initial condition (meaning: if there is an error or a power cut, the operator of the machine must empty the material from the automation, home the robot, even reset all the cylinders to their initial positions (with a homing program activated from the HMI), and then restart the machine. To prevent that, and make it more user-friendly, I'm thinking to implement a modular finite state machine where the different modules for the machine (material loading ports, doors, conveyors, robot) are all interlocked together. Having a background in PASCAL programming, it seems like going with ST language will be easier for me to get started in PLC programming. To begin, I've declared a series of global variables for each module, called STATE_<module-name>_CURRENT and STATE_<module-name>_NEXT, all of them set as unsigned int words, so they can store an integer value and I can use them with a CASE statement. Now, for clarity, I was planning on using global constants in those CASE statements. So, if I declare the constant ST_MACHINE_INIT as unsigned int word with value 0, typing ST_MACHINE_INIT should be the same as typing 0 in the CASE statement, and if ST_MACHINE_MANUAL_MODE is declared as a constant with a value of 1, it should be the same as typing 1, right? at least, in PASCAL (upon which the ST language seems to be based) would work like that. I have checked several manuals from Mitsubishi, but I didn't find anything in regard to that. They only say: CASE <variable> OF <value1>: <statement1>; <value2>: <statement2>; END_CASE; However, I've noticed that when I use a constant as value1 (declared as global labels with an unsigned integer value, same as the variables), GX Works 3 is giving me syntax errors after OF and after the statements (represented as ~). CASE <variable> OF~ <value1>: <statement1>;~ <value2>: <statement2>;~ END_CASE; If I replace the constant by the integer value, the syntax error goes away. It seems, then, that GX Works is not accepting constants as values. Is that the case? I prefer to use constants or variables with a fixed, known value instead of just typing the integers for code clarity and because they allow for posterior modifications easily. Does anyone have experience in this? Thanks.