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
YAML
Messaging
INSTALLATION
CONFIGURATION
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

LibreLogic

PLC-EMU is based around LibreLogic, a free PLC library. See https://github.com/kalamara/librelogic for reference.

NACS

The project configuration is done with NACS, Not Another Configuration System. See https://github.com/kalamara/nacs for reference.

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.

Build system

CMAKE 2.22 is required. ninja is used but other build tools can also be supported. Compilation is done currently on GCC 9

Operating system

Currently only Linux is supported.

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 ./Config.sh to configure the sources and then ./Build.sh to build.

This should create an executable named "plcemu" and a text file named "config.yml"

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.

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.

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.