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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.

Table of contents

OVERVIEW
DEPENDENCIES
Hardware
Comedi
User space
Simulation
YAML
Messaging
Unit testing
CAPABILITIES
INSTALLATION
CONFIGURATION
PROGRAMMING
Ladder Diagram
Instruction List
INTERFACE
Command Line
Distributed UI
ISSUES

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.

DEPENDENCIES

Hardware

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.

Comedi

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.

User space

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.

Simulation

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.

YAML

PLC-EMU configuration files are in YAML format, and so PLC-EMU v. 2 onwards depends on libYAML.
See the official project page
https://github.com/yaml/libyaml for details.

Messaging

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.

Unit testing

The PLC core library comes with a harness of hundreds of unit tests, however these tests require CUnit to run.
See
http://cunit.sourceforge.net/

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.

INSTALLATION

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

./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 enable the distributed user interface, you can configure with the option

/.configure --enable-ui

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   
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.

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.

LD Example : Triple Majority Circuit

; 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

IL Example : GCD

; 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

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

Command Line

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.

Supported commands:

START

start plc loop

STOP

stop plc loop

HELP

display help message

QUIT

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.

FORCE<sequence><index><value>

This will force a value on a sequence block for debugging purposes.

UNFORCE<sequence><index>

Reverts the FORCE command.

Distributed UI

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

/.configure --enable-sim

Example UI client

See cli-zmq.c for an example command line remote UI client that implements the same functionality as the default command line interface.

Legacy (ncurses)

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.

ISSUES

Please send feedback, questions, suggestions, requests, help(?) to:
(kalamara AT users.sourceforge.net)