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.
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.
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
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.
From version 2 onwards there are extensions for network distribution. Serialization of all network messages is done in YAML format, and the messaging layer is implemented using ZeroMQ.
Although networking extensions are disabled by default, to enable networking ZeroMQ is required.
See http://zeromq.org/ for details.
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.
Checkout a snapshot from github, or alternatively
download the tarball from www.sourceforge.net/projects/plcemu and unzip the source files in a directory.
Then run in superuser mode
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:
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
for text simulation mode.
If you want to enable the distributed user interface, you can configure with the option
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 PROGRAM: - 2 - INDEX: 0 ID: "gcd.il" #Digital Inputs DI: - 16 - INDEX: 0 BYTE: 0 ID: A - INDEX: 1 BYTE: 0 ID: B #Digital outputs DQ: - 2 - INDEX: 0 BYTE: 0 ID: OUTPUT #Memory registers (integers) MREG: - 4 - INDEX: 0 ID: RESULT VALUE: 64 - INDEX: 1 ID: TEMP #Memory variables (real numbers) MVAR: - 6 - INDEX : 0 ID : N VALUE : 1.0 - INDEX : 1 ID : MEAN - INDEX : 2 ID : M2 - INDEX : 3 ID : DELTA - INDEX : 4 ID : ONE VALUE : 1.0 #Timers TIMERS: - 2 - INDEX: 1 RESOLUTION: 10 PRESET: 10 #Blinking timers PULSES: - 2
Everything up to the PROGRAM tag, is system configuration.
The sequences from the PROGRAM tag onwards represent the logic blocks of the PLC.
The number after the block name represents the size of the block sequence, ie. how many block instances are allocated.
The key - value pairs after the size are the blocks' parameters.
INDEX represents the position of the specific block in the sequence, eg. input 5 would have INDEX: 5
ID is a unique string identifier for the specific block.
The rest are block - specific parameters.
These parameters can be edited in runtime.
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).
.ld files are in Ladder diagram format.
The version of LD PLC-EMU supports, consists of the following operators and
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.
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
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
'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----+
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:
Supported Operators are:
) close parenthesis (pop instruction from stack)
S set output
R reset output
JMP jump to label
Modifier symbols recognized are:
( open parenthesis (push instruction to stack)
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:
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;
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
The default UI for version 2.0 onwards is command line based.
This is just a std prompt where the PLC's internal state in YAML format is monitored, while PLC commands can be issued.
start plc loop
stop plc loop
display help message
close the UI
EDIT <sequence><index><key: value>
Edit a configuration for any input, output or other sequence block.
The key: value pair can be any of the parameters in the configuration of the specific block.
This will force a value on a sequence block for debugging purposes.
Reverts the FORCE command.
Optionally any kind of UI and any number of UI instances can be connected over zeromq sockets, locally or remotely.
The UI should continuously receive the PLC state in YML format in a PUB / SUB configuration, and asynchronously send commands in a REQUEST / REPLY fashion.
To enable remote UI, run
See cli-zmq.c for an example command line remote UI client that implements the same functionality as the default command line interface.
There are plans for reimplementing a ncurses based zeromq client with the same functionality as the legacy PLC-EMU UI.
Currently no ncurses dependency exists.