ASCII to PLC communication made easy

ASCII (American Standard Code for Information Interchange) started life in 1960 as the first widely adopted English character encoding for computers. Since 2008 the actual character encoding most of us rely on is UTF-8 but the original 128 printable characters many of still reply on a match from ASCII to UTF-8. If you are leveraging any form of character strings on the factory floor it’s most likely they are 128 characters of the original ASCII (we could call them ASCII or UTF-8, we personally think ASCII is cooler).

What role does ASCII play on the factory floor? ASCII based devices largely come from two camps. Devices that are text centric and devices that originally interacted with a PC based application.

Text Centric: Barcode Scanners, Weigh scales, Printers, RFID readers and LED Displays. These are devices that either read, or display human readable characters (ASCII).
ASCII Command Response: Many devices leverage ASCII strings do more than simply report or display data. They leveraged ASCII to create custom protocols top interface with their device(s). This was accomplished by defining a set of commands and responses. CMD:GO, RSP:OK. In industrial automation we leverage open protocols like Modbus, EtherNet/IP and PROFINET to move messages reliably. For many devices the interface between the node and PC was a custom ASCII protocol.

How Does ASCII Work In Automation?

Generally speaking. ASCII is challenging to deploy in an automated control system. While all PLCs can support a string (a group of ASCII characters), it’s very challenging to use ladder logic to filter and interpret the data. ASCII messages have no defined length or structure. Devices leverage features like start and end delimiters or CRC to define a message and ensure it is received properly. Parsing a message and calculating something like a CRC in your PLC logic is a bit like using a machete to spread butter on bread. It can work but it’s not advised and even success is fraught with risk.

The Best Way To Get ASCII Into A PLC

This is where gateways from RTA can save you time, money and headaches. Our gateways eliminate the most challenging elements of leveraging ASCII in PLCs. The gateway will determine what a message consists of by delimiters, length or timing. It will then pass only the payload of data, without any delimiters to the PLC. Better yet it can parse a message into individual data points or concatenate multiple date points from a PLC into an ASCII string. Your PLC only deals with data values, not the challenges or turning ASCII characters into usable data.

These solutions work for ASCII over serial 232, 485, or 422, Ethernet or USB.