Jargon file

The Jargon page!

This page has some of the Jargon and buzz-words I've used on the site explained, which is kinda handy.

There are links to this page scattered throughout the site, use your browsers 'Back' button to return to whence you came.

Without further adieu, The jargon:


Comma Seperated Value.

A text based file format which is handy for getting data into and out of spreadsheets of data base applications.

More reading: wikipedia CSV


Human Machine Interface

Software or hardware system that allows the user (Human) to interact with the PLC/RTU system (Machine). This may be a dedicated hardware panel with screen and controls such as a thermostat controller in a large air conditioning system or a SCADA system running on a computer.

More reading: wikipedia HMI


This is the interface standard I've used. You can find a spectacular amount of info on the modbus website including the standard specification documents and an active forum of users and developers.

The modbus standard includes definitions for the physical cabling, data encoding and application level protocol for serial and ethernet / IP based communication for for distributed automation systems. Read all about it on their website, I don't want to spend all day typing!


Protocol Data Unit. (frame)

The protocol data unit in modbus refers to one packet or unit of data, consisting of a function code and the data for that function code.

There is also reference to the the 'modbus serial line PDU' on some sites (and in the standard) which refers to the whole of the data frame sent over serial line modbus, including the address field, modus PDU and a CRC word for error-checking.

I have liberally used the term 'frame' in place of PDU on this site.


PIC is a generic name for microcontrollers from Arizona Microchip. The name comes about because the first three letters of the part numbers for their controllers is 'PIC'.

In particular I am using the PIC16F870 for the development of my first RTU. I intend to also use the PIC16F88 for smaller units where just one input or output type or function is required.


Programmable Logic Controller

A dedicated computer / microcontroller that is used for automation and monitoring tasks. PLC can also refer to a dedicated software package running a 'virtual PLC' on a standard desktop or industrial PC.

More reading: wikipedia PLC


Remote Terminal Unit.

Basically the remote or slave controller(s) in a distributed automation system. Generally you'd have a number of RTUs connected to one master. The master could be a PLC, data logger, or a PC running SCADA or HMI software.

More reading: wikipedia RTU


Supervisory Control And Data Acquisition

This one gets used in all sorts of places, but I'm using it to describe a bit of software you run on a PC to monitor and control a group of PLCs and RTUs that make up an automation system.

Generally an SCADA system would provide some sort GUI interface, and provide trending/hitorical information as well as real time monitoring and possibly control of the automation system.

More reading: wikipedia SCADA

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