I have always been an old school programmer. Hardware in front of you hooked up to all of the I/O. I have recently looked at the automation direct do-more designer software solution. The Do-More Designer Software will allow you to build your ladder logic, download into a simulator (comes with the software) and run the code. The price of all of this… FREE
I will not get into a lot of details because the documentation available already will get you through the software step by step.
– Download the software
– Install the software
– Use the YouTube videos for help with getting around the software and making your first program.
The following are several links to help you discover the plc programmer in you:
If you have any questions or need further information please contact me.
Thank you,
Garry
If you’re like most of my readers, you’re committed to learning about technology. Numbering systems used in PLC’s are not difficult to learn and understand. We will walk through the numbering systems used in PLCs. This includes Bits, Decimal, Hexadecimal, ASCII and Floating Point.
To get this free article, subscribe to my free email newsletter.
Use the information to inform other people how numbering systems work. Sign up now.
The ‘Robust Data Logging for Free’ eBook is also available as a free download. The link is included when you subscribe to ACC Automation.
The term I/O means Input/Output. I/O can come in two different types; Discrete or Analog Most people starting out leaning about programmable logic controls (PLC) are taught all about discrete input and outputs. Data is received from devices such as push-buttons, limit-switches etc. and devices are turned on such as motor contactor, lights, etc. Discrete input and output bits are either on or off. (1 or 0) The following program will show a motor control circuit stop start. Motor off:
Motor on:
Analog inputs Common input variables for analog are temperature, flow, pressure, etc. They are converted to an electrical signal into a PLC analog input. Standard electrical signals are 0 – 20 mA, 4 – 20 mA, 0 – 10 volts DC, -10 – 10 volts DC. Note: It is recommended that a 4 – 20 mA signal is best. If voltage is required, a resistor can be added to get a voltage input. Analog outputs Common output variables for analog are speed, flow, pressure, etc. They are converted from a word in the PLC to the output of the analog. The range of signal is then outputted to the device to control the position, rate, etc. Standard electrical signals to the device are 4 – 20 mA, 0 – 10 volts DC, -10 – 10 volts DC. Both Analog Inputs and Outputs use words to determine the signal going to or from the device. Example: 4 – 20 mA current Input – 8 bit resolution 4 mA = 000000002 = 0016 20 mA = 111111112 = FF16 Example: 4 – 20 mA current Output – 8 bit resolution 0016 = 000000002 =4 mA FF16 = 111111112 =20 mA For a review of numbering systems, follow the link below: What everyone should know about PLC numbering systems
Let me know if you have any questions or need further information.
Thank you,
Garry
If you’re like most of my readers, you’re committed to learning about technology. Numbering systems used in PLC’s are not difficult to learn and understand. We will walk through the numbering systems used in PLCs. This includes Bits, Decimal, Hexadecimal, ASCII and Floating Point.
To get this free article, subscribe to my free email newsletter.
Use the information to inform other people how numbering systems work. Sign up now.
The ‘Robust Data Logging for Free’ eBook is also available as a free download. The link is included when you subscribe to ACC Automation.
Grey Code
Grey Code is used because only one bit of data will change at a time. The following chart shows the conversion of Grey Code to Binary.
Number
Binary Code
Grey Code
Number
Binary Code
Grey Code
0
0000
0000
8
1000
1100
1
0001
0001
9
1001
1101
2
0010
0011
10
1010
1111
3
0011
0010
11
1011
1110
4
0100
0110
12
1100
1010
5
0101
0111
13
1101
1011
6
0110
0101
14
1110
1001
7
0111
0100
15
1111
1000
It is important for absolute encoders because if the power is interrupted the encoder will know where it is within the one bit.
Example:
Power is interrupted when the encoder is between 7 and 8. If we are looking at Binary Code all of the bits would be effected and we would not be sure as to what number we are looking at for the encoder. Therefore we have lost position. In Grey Code only one bit changes so we will still be able to tell if we were on 7 or 8 if the power was interrupted.
The following sample PLC program will convert 4 bit grey code into binary code.
This code was written in an Automation Direct PLC software called Do-more Designer.
Contact me for the above program. I will be happy to email it to you.
Thank you,
Garry
If you’re like most of my readers, you’re committed to learning about technology. Numbering systems used in PLC’s are not difficult to learn and understand. We will walk through the numbering systems used in PLCs. This includes Bits, Decimal, Hexadecimal, ASCII and Floating Point.
To get this free article, subscribe to my free email newsletter.
Use the information to inform other people how numbering systems work. Sign up now.
The ‘Robust Data Logging for Free’ eBook is also available as a free download. The link is included when you subscribe to ACC Automation.
Programmable Logic Controllers (PLC) are the same as computers. They only understand two conditions; on and off. (1 or 0 / Hi or Low/ etc.) This is known as binary. The PLC will only understand binary but we need to display, understand and use other numbering systems to make things work. Let’s look at the following common numbering systems.
Binary has a base of two (2). Base means the number of symbols used. In binary the symbols are 1 or 0. Each binary symbol can be referred to as a bit. Putting multiple bits together will give you something that looks like this: 100101112. The 2 represents the number of symbols/binary notation. Locations of the bits will indicate weight of the number. The weight of the number is just the number to the power of the position. Positions always start at 0. The right hand bit is the ‘least significant bit’ and the left hand bit is the ‘most significant bit’.
Let’s look back at our example to determine what the value of the binary number is:
100101112 =
We start with the least significant bit and work our way to the most significant bit.
1 x 20 = 1 x 1 = 1
1 x 21 = 1 x 2 = 2
1 x 22 = 1 x 2 x 2 = 4
0 x 23 = 0 x 2 x 2 x 2 = 0
1 x 24 = 1 x 2 x 2 x 2 x 2 = 16
0 x 25 = 0 x 2 x 2 x 2 x 2 x 2 = 0
0 x 26 = 0 x 2 x 2 x 2 x 2 x 2 x 2 = 0
1 x 27 = 1 x 2 x 2 x 2 x 2 x 2 x 2 x 2 = 128
100101112 = 1 + 2 + 4 + 16 + 128
100101112 = 151
Note that the we just converted the binary number to our decimal numbering system. The decimal numbering system is not written with a base value of 10 because this is universally understood.
To be sure we have the concept down, let’s take a look at our decimal numbering system the same way as we did the binary.
Decimal has a base of ten (10). The symbols are 0, 1, 2, 3, 4, 5, 6, 7, 8 and 9.
15110 =
1 x 100 = 1 x 1 = 1
5 x 101 = 5 x 10 = 50
1 x 102 = 1 x 10 x 10 = 100
15110 = 1 + 50 + 100
151 = 151
Hexadecimal has a base of sixteen (16). The symbols are 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, A, B, C, D, E and F. Hexadecimal is used to represent binary numbers. F16 = 11112
Every for bits of binary represent one hexadecimal digit.
In our original binary number we now can convert this to hexadecimal.
100101112
The least significant four bits are:
01112 =
1 x 20 = 1 x 1 = 1
1 x 21 = 1 x 2 = 2
1 x 22 = 1 x 2 x 2 = 4
0 x 23 = 0 x 2 x 2 x 2 = 0
01112 = 1 + 2 + 4 + 0 = 716
The most significant four bits are:
10012 =
1 x 20 = 1 x 1 = 1
0 x 21 = 0 x 2 = 0
0 x 22 = 0 x 2 x 2 = 0
1 x 23 = 1 x 2 x 2 x 2 = 8
10012 = 1 + 0 + 0 + 8 = 916
Therefore:
100101112 = 9716
We can now convert this hexadecimal number back into decimal
9716 =
7 x 160 = 7 x 1 = 7
9 x 161 = 9 x 16 = 144
9716 = 7 + 144 = 151
The following chart will show all of the combinations for 4 bits (nibble) of binary. Its shows the Binary, Decimal and Hexadecimal (Hex) values. It is interesting to not that Hex is used because you still have only one digit (Place Holder) to represent the nibble of information.
Binary
Decimal
Hexadecimal
Binary
Decimal
Hexadecimal
0000
00
0
1000
08
8
0001
01
1
1001
09
9
0010
02
2
1010
10
A
0011
03
3
1011
11
B
0100
04
4
1100
12
C
0101
05
5
1101
13
D
0110
06
6
1110
14
E
0111
07
7
1111
15
F
ASCII (American Standard Code for Information Interchange)
Two nibbles (8 bits of data) together form a byte. A byte is what computers (PLC) use to store and use individual information. So it will take one unique byte to represent each individual numbers, letters (upper and lower case), punctuation etc. www.AsciiTable.com
Example:
Chr ‘A’ = 4116 = 010000012
Chr ‘a’ = 6116 = 011000012
Chr ‘5’ = 3516 = 001101012
Each time you hit a key on your keyboard, the following 8 bits of data get sent.
A word ismade up of two bytes, or 4 nibbles, or 16 bits of data. Words are used in the PLC for holding information. The word can also be referred to as an integer.
Long word / Double word is made up of 4 bytes, or 8 nibbles, or 32 bits of data. Long words are used for instructions in the PLC like math.
Hey what about negative numbers?
So far we have talked about unsigned words. (Positive numbers)
Signed words can hold negative numbers. Bit 15 (most significant bit) of a word is used to determine if the word is negative or not.
The following table shows you the signed vs unsigned numbers that can be represented in the PLC.
HEX
8000
BFFF
FFFE
FFFF
0000
3FFF
7FFE
7FFF
Signed
-32768
-16385
-0002
-0001
00000
16383
32766
32767
Unsigned
32768
49151
65534
65535
00000
16383
32766
32767
Memory retentiveness:
When working with PLC’s look at the memory tables to determine what will happen if power is removed from the device. Will the bits go all off or retain their prior state?
Usually there will be areas that can be used in the PLC for both conditions.
As you can see PLC numbering systems and computers are very much related and it all boils down to individual bits turning on and off. The interpretation of these bits will determine what the value will be.
Let me know your thoughts, or questions that you have on PLC numbering systems.
Thank you,
Garry
If you’re like most of my readers, you’re committed to learning about technology. Numbering systems used in PLC’s are not difficult to learn and understand. We will walk through the numbering systems used in PLCs. This includes Bits, Decimal, Hexadecimal, ASCII and Floating Point.
To get this free article, subscribe to my free email newsletter.
Use the information to inform other people how numbering systems work. Sign up now.
The ‘Robust Data Logging for Free’ eBook is also available as a free download. The link is included when you subscribe to ACC Automation.
