LDmicro and Arduino

Ladder Logic for Arduino.

In this article the way how to run program in ladder logic from LDmicro on Arduino is presented. LDmicro is free SW to write and simulate ladder logic programs. When is ladder logic program is successfully simulated it could be compiled for AVR or PIC processor. However ATmega used in Arduino is not supported. Fortunately LDmicro can “compile” code into ANSI C. So, let’s take a look how we can run this code on Arduino.

Little Background

When we select ANSI C Code as Microcontroler type in Settings menu of LDmicro after compile we will get C file. This file contains all logic but it requires header file ladder.h which is missing. So, we have to implement this file. Let say we have input contact called “button” then we have to implement function:

BOOL Read_U_b_Xbutton(void) {
 return digitalRead(10); // button on digital pin 10
}

And similar to others input and output pins. Actually we have to write the layer between leader logic program and real HW of Arduino. And it could be more than simple call of digitalRead or digitalWrite. For example we could control servos, read data from proximity sensor and so on. Ability to write this layer is very powerful. Ladder logic could be used for core logic of application and C only for HW layer.

For more information read actual generated C file. It contains more information.

Generating ladder.h

If we need just direct control of digital IO pins of Arduino ladder.h could be easily generated for us. I wrote PHP script that can do this job. It requires generated code and mapping between variable name we use in ladder logic and pin numbers of Arduino. It will generate ladder.h with all nessesary functions and setup function (correctly calls pinMode for all used digital pin). Script could be used as console application or it’s also available online.

Step by step

Let’s do it step by step. Complete example is available for download.

1. Write code in LDmicro.

2. Select as Microcontroller “ANSI C Code”.

3. Compile it as ladder.cpp (save it as *.cpp file not *.c, otherwise Arduino won’t compile it)

4. Prepare mapping for IO pins of Arduino. Its text file called pinmap.ini. See example for details.

5. Generate ladder.h file by ladder-gen.php.

Tip: Ladder.h generator is available also online. However you can’t use pinmode.ini in online version. So all input and output pins have to have name “d0” for arduino digital pin 0, “d1” for pin 1 and so on.

6. Create Arduino sketch.

#include "ladder.h"

void setup() {
    PlcSetup();
}

void loop() {
    PlcCycle();
    delay(10);
}

See example for better sketch implementation (this one is for illustration and it's not accurate for timers).

7. Compile it by Arduino editor and upload it.

8. That’s all.

Tip: Now if you enable “External editor” setting of Arduino editor then you need just hit “F5“ in LDmicro and then push “Upload “ in Arduino editor to run program.

Conclusion

I hope presented method will help you start with ladder logic for Arduino. If you have any suggestion or find a bug in script, let me know.

Arduino Predefined Constants

There are a lot of #define-d constants in Arduino. Most of them are from avr-gcc compiler but some are also Arduino specific. Let’s take a look at some interesting ones.

Gcc constants

__DATE__and __TIME__

Date and time of compilation.

__FILE__and __LINE__

FILE is full path to current compiled file and LINE is current line number inside this file. However FILE is not *.pde (sketch file), it’s *.cpp. If you don’t know how Arduino build process works you will probably don’t need to use this constants. However it would be useful in libraries.

__func__

Name of current function.

void setup()
{
 Serial.println(__func__); // prints "setup"
}

__COUNTER__

Every time you use this one, it increases its value.

Serial.println(__COUNTER__); // 0
Serial.println(__COUNTER__); // 1
Serial.println(__COUNTER__); // 2

CPU Type and How to Determine Arduino Bord

According to selected target processor, compiler defined constant by processor name.

Constant	CPU	Board
__AVR_ATmega168__	ATmega 168	Arduino Decimilia and older
__AVR_ATmega328P__	ATmega 328P	Arduino Duemilanove and Uno
__AVR_ATmega1280__	ATmega 1280	Arduino Mega
__AVR_ATmega2560__	ATmega 2560	Arduino Mega 2560
__AVR_ATmega32U4__	ATmega 32U4	Arduino Leonardo
__SAM3X8E__	AT91SAM3X8E	Arduino Due

So by testing of these constants you can determine board type. For example:

#if not (defined(__AVR_ATmega2560__) || defined(__AVR_ATmega1280__))
    #error Sorry dude, this program works only on Arduino Mega 
#endif

Another example is in sketch in the end of article.

Arduino Specific Constant

Arduino compiler define these constants

ARDUINO

Version of Arduino SW. So if you use Arduino 0022 you wil get:

Serial.println(ARDUINO); // 22

F_CPU

Frequency of oscillator on the board (in hertz). For example on Arduino Uno you will get:

Serial.println(F_CPU); // 16000000

Try it

You can try example sketch on your board.