new to plc's -need easy q answered

[Guest lizardtoe]

I apologize in advance for tossing out such an easy question...ALL of my programming experience is in text based code. 1-what is the difference between a tag and a register? 2-what kind of data can be stored in a tag/register? 3-how is information that is stored in a tag or register transmitted to a device (hmi) ---IE. is it simply a matter of on/off signals like I/O outputs? 4-I have zero experience with ASCII...what is it and what does it do? ANY help or advice is welcome -this includes partial answers or references

[KinK]

A tag is a name applyed to a memory area. A register is normaly used for data storage ie shift register I think thats what you are talking about, a group of memory areas that are used for data storage move something into the first and all the others should move down one spot and the last one goes away. what kind of data can you store well that depends on what plc you are using and where in the memory area you store it. normaly PLC's have more than one type of memory area. it can be Boolean or an int or uint or ...... (American Standard Code for Information Interchange) -- This is the de facto world-wide standard for the code numbers used by computers to represent all the upper and lower-case Latin letters, numbers, punctuation, etc. There are 128 standard ASCII codes each of which can be represented by a 7 digit binary number: 0000000 through 1111111, plus parity.

[Jay Anthony]

ASCII Reference Table @ MrPLC.com ASCII Master @ MrPLC.com

[Guest]

Greetings lizardtoe, my distinguished colleague KinK has gotten you started ... and I see that Jay Anthony (also distinguished) has given you a helpful link while I've been typing ... let me add just a slightly different angle ... I’ll try to keep this as “dirt simple” as I can ... once you’ve gotten some more experience under your belt, you’ll be able to pick out the finer points where Kink was “more right” and I was “more wrong” ... 1-what is the difference between a tag and a register? in most cases: none ... at the very beginner stage, they are the same ... each one is just a place (a “location” ... a “box”) in a computer’s memory that can hold some piece of information ... and keep in mind that a PLC !IS! a type of computer ... it’s just that some manufacturers call their variable locations “tags” (or “tagnames”) ... while other manufacturers call their variable locations “registers” ... 2-what kind of data can be stored in a tag/register? as KinK said, it depends ... common types of stored information are “integers” (whole numbers with no fractional parts) ... and “floating point” values (numbers which CAN have fractional parts) ... ASCII information (often called “strings”) ... these are like strings of text for example: “hello world” ... and also “discrete” information can be stored in a tag or a register ... “discrete” is also commonly called “digital” or “Boolean” type data ... basically it just means a piece of information that can ONLY be ON or OFF ... this is usually represented in a tag or register by a value of either a “1” or a “0” ... 3-how is information that is stored in a tag or register transmitted to a device (hmi) ---IE. is it simply a matter of on/off signals like I/O outputs? to answer your question specifically, we need to know exactly what type of hardware you’re using ... and how the pieces of hardware are connected together for communications purposes ... one very common buzzword here is “DDE” ... this stands for “Dynamic Data Exchange” ... this is a Microsoft term which basically means “one Windows program TALKING to another Windows program” ... one common setup is to have the PLC connected to the HMI by a cable ... and then program the PLC (at one end) and the HMI (at the other end) to “share” data back and forth (often by using DDE) over the network ... and no, it doesn’t always have to be just off and on data ... it can also be analog values such as temperatures and flow rates, etc. ... once again, this is a VERY big topic ... so tell us how your system is set up and we’ll try to provide more details ... 4-I have zero experience with ASCII...what is it and what does it do? basic beginner’s idea: think of ASCII as “text” ... this is the format that is commonly transmitted from a barcode reader to a computer ... or from a computer to a printer ... in simplest terms, the ASCII data doesn’t have a numeric VALUE ... it is just a pattern of characters ... something like “hello world” would be a common example ... if you come from a "structured language" programming background, then you've probably always referred to ASCII information as "strings" ... once again, all of this is being kept on a very basic level - that's what you asked for ... there are some exceptions to these "rules" which will become evident as you gain experience ... I hope this helps ... and welcome to the forum ... best regards, Ron Edited October 4, 2004 by Ron Beaufort

[KinK]

well said Ron wow are your fingers bleeding yet that was a great answer.

[Jay Anthony]

Thanks, Ron Beaufort, for going back to basics on these subjects. You know if we could somehow put all this combined knowledge into a smart pill, we could have one heck of an on-line pharmacy!!

[Sergei Troizky]

Sorry for correcting you, Ron, but a tag in HMI is not always a register. It may be a bit also. And, actually a tag is neither of them. It is a named reference to a PLC device.

[KinK]

LOL ok it will get very confusing if we get into everything that has a tag... TAG is just a name/Lable given to something else. kind of like KinK is my tag, it is not my real name but everyone here knows me by it I could be a meat popsicle, or a Machine, or a computer named hal but my tag here is KinK I realize that this can and will be confusing but most instrumentation and or controls have a Tag name it is a name that is easyly identifyable and is used to identify equipment, memory, datapoints ect. thats about the best I can do explanining it. Edited October 27, 2004 by KinK