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PLC-EMU is a Programmable Logic Controller EMUlator for automation applications on linux with digital/analog IO cards, with C functions, Ladder Diagrams,or IEC61131-compliant Instruction List/Structured Text. It is a cheap and open alternative to PLCs. project_screenshots project_admins
[TOC]
#1. OVERVIEW
PLC-EMU stands for Programmable Logic Controller EMUlator. This means PLC-EMU is a tool for emulating PLCs on a Linux box, using I/O cards. This way you can build a cheap alternative to PLC's, for use with automation applications.
#2. DEPENDENCIES/RECOMMENDATIONS
First of all, you need to install one or more digital I/O cards.
PLC-EMU works in two modes: through comedi, and in user space.
Additionally, File Simulation mode is supported in case no hardware is available.
In Comedi mode, all you need to do is install and set up the apropriate Comedi driver for your card, and copy the setup values to PLC-EMU's config file. Consult www.comedi.org for a list of compatible cards, and instructions on comedi.
In user-space mode, you need to know the base IO address space of your cards, and which area of it the card uses for reading (read offset) and writing (write offset). For pci cards, run
lspci -vvv
to find out the base address. The rest should be found in the cards' manual.
In File Simulation mode, PLC-emu can be configured to read input bytes from an ASCII text file and send outputs to another text file.
#3. CAPABILITIES
PLC's are real time controllers whose function is to periodically read inputs, run several real time tasks, and control outputs, in a steady time period, which in commercial PLC's varies usually from 2 to 10 milliseconds. PLC's are the standard platform for automation applications, and can they can be programmed in one or more of the 4 programming languages as defined by IEC116131-3: Instruction List, Ladder Diagram, Function Block Diagram, or Structured Text.
PLC-EMU emulates this function: In a configurable time cycle, it will read the inputs from your card, run a task as programmed by the user, and send the appropriate outputs back to the card.
Apart from inputs and outputs, PLC-EMU also holds an internal "address space" of a user-defined number of memory variables which you may use in your programs.
It also supports Timer and Blinking Timer (Pulse) registers, whose number and function can as well be configured by the user.
#4. INSTALLATION
Download the tarball from www.sourceforge.net/projects/plcemu
Unzip the source files in a directory and run in superuser mode
./configure; make; make install
This should create an executable named "plcemu" and a text file named "config.yml"
If you dont have the comedi libraries, run configure with the option:
/.configure --enable-uspace
Note that you dont need this if you have the comedi libraries, but you havent set up comedi for some reason.
If you don't have actual hardware, run configure with the option
/.configure --enable-sim
for text simulation mode.
If you want to work with a stdout (printf) based user interface, you can configure with the option
/.configure --disable-ui #5. CONFIGURATION
Edit a config.yml file, which holds configuration variables and their values in yml format.
An example config.yml as included:
STEP: 10 #time cycle in milliseconds PIPE: plcpipe #UNIX path of named pipe polled for commands
#hardware HW: STDI/O #just a text tag that appears in a footer
#user space interface: USPACE: BASE: 50176 #hardware address base WR: 4 #write offset RD: 0 #read offset
#COMEDI interface: COMEDI: FILE: 0 #device and subdevice nodes of comedi driver. SUBDEV: IN: 0 OUT: 1
#SIMULATION IO SIM: INPUT: sim.in OUTPUT: sim.out
#PROGRAM
DI:
- 16
- INDEX: 0
BYTE: 0
ID: A
- INDEX: 1
BYTE: 0
ID: B
DQ: - 2 - INDEX: 0 BYTE: 0 ID: OUTPUT
MREG: - 4 - INDEX: 0 ID: RESULT VALUE: 64
- INDEX: 1
ID: TEMP
PROGRAM: - 2 - INDEX: 0 ID: "gcd.il"
#6. PROGRAMMING
You can edit a text file with a task in LD or IL in your favorite text editor and then load it into PLC-EMU (see below).
###Ladder Diagram .ld files are in Ladder diagram format. The version of LD PLC-EMU supports, consists of the following operators and operands.
Operators These are the accepted symbols that can exist along with the operands.
'-' propagates a boolean state horizontally, from left to right. Thus, it works as a logical "AND".
'+' changes line and can join states of up to 3 different lines, like a logical "OR" .
'|' propagates a state vertically, both ways between aligned "+" nodes.
'!' negates the state of the following operand like a logical "NOT"
'(' open contact. this propagates a state directly to an output. the following operand must be an output.
')' negate contact. this propagates the opposite of a state to an output. the following operand must be an output.
'[' set coil. if this is ON, thestate of an output is set. the following operand must be an output.
']' reset coil. if this is ON, thestate of an output is reset. the following operand must be an output.
';' end of line. anything after that is considered "comments".
Blank characters interrupt lines, so be careful.
Input operands These can appear anywhere in a line before a '(', followed by a valid non negative index. Valid values of indexes are dependant on the operand and the configuration. This means, that if you have 16 timers and 64 inputs, you can write t14 and i62, but not t45 or i567. In every cycle, their values are polled and propagated to the diagram. Accepted symbols (case sensitive) are:
'i' digital input state
'q' digital output state
'r' rising edge of digital input
'f' falling edge of digital input
'm' pulse state of counter
't' output of timer
'b' output of blinker
'c' true, if serial input byte equals following index
Output operands These symbols must follow operator '(' and be followed by a valid index. Each output operand should appear only once.
'Q' digital output
'M' pulse of counter
'T' timer
'W' write following number to serial output.
; triple majority circuit ; https://en.wikipedia.org/wiki/Triple_modular_redundancy
i0---i1----+---------(Q0 i2---i0----+ i1---i2----+
###Instruction List
Alternatively, you can define a IEC61131-3 compatible Instruction List program in .il files. Currently, subroutines are not implemented. Just like standard Instruction List, all instructions store their result to an internal Accumulator register, while "ST" stores the Accumulator's value to its operand. A line of an IL program, shall follow the format:
[label:]<operator>[<modifier>[%<operand\><byte>[</bit>]]|<label>][;comment]
Supported Operators are: ) close parenthesis (pop instruction from stack) S set output R reset output AND OR XOR LD load ST store ADD SUB subtract MUL multiply DIV divide GT > GE >= NE <> EQ == LE <= LT < JMP jump to label Modifier symbols recognized are: ( open parenthesis (push instruction to stack) ! negate ? conditional Operands are the same as in LD, with the difference that it is assumed that they are Words (unsigned Integers), unless noted otherwise with the symbol '/'. As defined in the IEC standard, each instruction supports its own set of data types and modifiers, according to the following scheme:
| Instruction | Modifiers | Data Types |
|---|---|---|
| ) | N/A | N/A |
| S | N/A | BOOL |
| R | N/A | BOOL |
| AND | !,( | BOOL/WORD |
| OR | !,( | BOOL/WORD |
| XOR | !,( | BOOL/WORD |
| LD | ! | BOOL/WORD |
| ST | ! | BOOL/WORD |
| ADD | ( | BOOL/WORD |
| SUB | ( | BOOL/WORD |
| MUL | ( | BOOL/WORD |
| DIV | ( | BOOL/WORD |
| GT | ( | BOOL/WORD |
| GE | ( | BOOL/WORD |
| NE | ( | BOOL/WORD |
| EQ | ( | BOOL/WORD |
| LE | ( | BOOL/WORD |
| LT | ( | BOOL/WORD |
| JMP | ? | CHARACTER STRING |
; greatest common divisor ; https://en.wikipedia.org/wiki/Euclidean_algorithm
LD %i0
ST %m0
EQ %m3
JMP?end
LD %i1
ST %m1
EQ %m3
JMP?end
while:LD %m0 ; A
EQ %m1 ; A == B
JMP?endwhile ; while(A != B)
LD %m0
LT %m1 ; A < B
JMP?reverse
LD %m0
SUB %m1 ; A - B
ST %m0 ; A = A - B
JMP while
reverse:LD %m1 ; B
SUB %m0 ; B - A
ST %m1 ; B = B - A
JMP while
endwhile:LD %m0 ;
ST %q0 ; output gcd
end: LD %m3;
##C "API"
TBD
#7. INTERFACE
Executing plcemu from the command line
Usage: plcemu [-c config file] [-h]
Options:
-c uses a configuration file like the one described in section 5, other than config.yml
-h displays this help file
#8. ISSUES
Please send feedback, questions, suggestions, requests, help(?) to: (kalamara AT users.sourceforge.net)