Bit Game

Think of PLC memory as a cabinet with drawers called Registers. Data is held in these Registers. These Registers come in different sizes, and hold different kinds of data.

1 Bit = 0 or 1

1 Byte = 8 Bits

Bit:

Can have values 1 or 0. 1 typically represents On while 0 represents Off. Bits are the building block for all other types of data.

Integers: 

Whole numbers (no decimal points). Called: Integers (int), long Integers (long int) or Words. Look for the bit size and whether they are signed or unsigned. Unsigned are positive numbers, while signed are positive or negative.

Addresses in PLC - Allen-Bradley (N7:0), Siemens (MW0), ABB (MW0.0), Mitsubishi (D0) 

Floating point numbers:

Numbers with decimal points, and can be positive or negative. They are called floating point numbers (Float) or Real Numbers with their larger variety called double floats.

Addresses in PLC - Allen-Bradley (F8:0), Siemens (MD0), ABB (MD1.0), Mitsubishi (Z0)

Hexadecimal Format (Hex):

Instead of writing every bit out, it is common to group sets of 4 bits together. Each group can have a value of 0 – 15, which causes a problem since our number system goes from 0 – 9, so we also use A, B, C, D, E and F to get a total of 16 values. (0, 1, 2, 3, 4, 5, 6, 7, 8, 9 , A, B, C, D, E, F)

Example 1001 0011 1111 0010 in Hex would be 93F2

To be clear that we’re using Hex format we tack on a ‘0x’ the the start of the number so our last example would be written 0x93F2

Characters:

Typically 8 bit unsigned integers are often used to represent letter or symbols. Example: you may use them to display text on an operator panel. Use an ASCII table to see how values are mapped to symbols.

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