Back to tutorials
Beginner

PLC Programming Computational Mathematical Instructions – MOD | Modulo

By
Vladimir Romanov
Table of Contents

Introduction

The MOD, also known as the modulo, is an instruction which allows the user to calculate the remainder produced by a division of two integers. This instruction is not frequently used in ladder logic programming but is very useful for calculating the remainder of a ratio, production excess, and several other parameters. The instruction takes three registers as operands. The first two are the dividend and the divisor. The result is stored in this third register which is labeled as the destination.

This instruction can be found in situations which require one to find the leftovers of a batch, how the performance of a piece of machinery is or any other situation which relies on a notion of a remainder.

Example & Usage of MOD

Here’s a real-world scenario of a MOD instruction:

  1. A CompactLogix L24ER Allen Bradley PLC is used to control a process.
  2. In rung 0, a MOD  instruction is used to compute the modulo of an integer System_DINT[0] and System_DINT[1] and store the result in the integer System_DINT[2].
  3. Since the value of the first double integer is set to 200 and the second one to 43, the modulo evaluates to 26. In other words, 200 / 43 = 4 with a remainder of 26.
  4. In rung 1, a MOD  instruction is used to compute the modulo of an integer System_REAL and System_REAL and store the result in the float System_REAL[2].
  5. Since the value of the first double integer is set to 200.22 and the second one to 10, the modulo evaluates to 0.22. In other words, 200.22 / 10 = 20 with a remainder of 0.22.
  6. In rung 2, a MOD  instruction is used to compute the modulo of a system which calculates the remainder of a production run. “Source A” is set to the total number of cases produced while “Source B” has the count of products per case. By calculating the modulo, we can figure out if we’ve filled all cases or we have leftover product.

Programming example in Studio 5000:

MOD Modulo Instruction RSLogix 500 5000 Studio Tutorial Ladder Logix Programming

Outcome:

The MOD instruction will compute the remainder of a division of two integers or floats. In the first two examples, we’re calculating two remainders which evaluate to 28 and 0.22 respectively. These calculations can be confirmed through a simple calculator. The last rung is used to figure out if we have any leftover product. A simple example would be the production if 1023 bottle of beer while each case holds 25 bottles. Simple math allows us to evaluate a modulo of 23 which should be utilized to complete the run.

The MOD instruction is not something you’d see on a regular basis in ladder logic but can be very useful in niche situations.

Data Types Allowed for MOD

The MOD can be used to compare two values of identical types or mismatching types such as float and integer. These value can be INTs or FLOATs.

  • Integer – You may specify each operand to be of “Integer” type.
  • Float – You may specify each operand to be of “Float” type.

Video Tutorial

Back to tutorials

Related Tutorials

Intermediate

MicroLogix 1100 RSLogix 500 External IO PLC Programming Tutorial

The MicroLogix 1100 PLC is still heavily used in the industry and is one of the most recommended PLCs for learning PLC programming. The MicroLogix 1100 PLC is compact, offers a variety of I/O configurations and is inexpensive relative to other Rockwell options. Furthermore, the MicroLogix 1100 PLC is programmable using the free version of RSLogix 500 that can be downloaded from the official Rockwell website.

By
Vladimir Romanov
Beginner

PLC Simulator - PLC Programming & Testing within a Simulated Environment

A PLC Simulator is an excellent avenue to practice PLC ladder logic programming. Although the software environment is not the perfect substitute for hands on experience on an actual PLC, the simulation delivers a very accurate representation of ladder logic execution.

By
Vladimir Romanov
Intermediate

HMI Software - Different Tools, Applications and Solutions to Meet Your Needs

HMI Software is commonly referred to as the development application that will be used to create the runtime application for an HMI terminal. It’s important to understand this distinction as we will be going over the HMI development environments used by PLC and HMI programmers to create the screens rather than the end-user applications you will see at the plant level.Numerous HMI programming software solutions are found on the market. Although they aim to achieve the same result, different packages have a distinct advantage over others in terms of price, reliability, ease-of-use and technical capability. It is therefore possible to find the right solution that will fit your specific application if you spend the time to research all options.

By
Vladimir Romanov