Constant Expressions

Boolean

• These are the Boolean reserved keywords:
  • TRUE
  • FALSE
• See Valid Constant Expressions for an example.

32-bit (default) Integer

• 32-bit integer constant expressions must be valid numbers between -2147483648 to 2147483647.
• DINT is the default size for integers: such constant expressions do not need any prefix.
• Use 2#, 8#, or 16# prefixes to specify an integer in binary, octal or hexadecimal basis, respectively.
• See Valid Constant Expressions for an example.

16-bit Integer

• 16-bit integer constant expressions are valid integer values (between -32768 and +32767).
• Must be prefixed with INT#.
• All integer expressions having no prefix are considered DINT integers.
• See Valid Constant Expressions for an example.

Long (64-bit) Integer

• Long integer constant expressions are valid integer values.
• Must be prefixed with LINT#.
• All integer expressions having no prefix are considered DINT integers.
• See Valid Constant Expressions for an example.

Double Precision Floating Point Value

• Real constant expressions must be valid numbers, must include a dot (.).
• If you need to enter a real expression having an integer value, add .0 (dot zero) at the end of the number.
• You can use F or E separators for specifying the exponent in case of a scientific representation.
• LREAL constants are limited to 14-15 digits of accuracy.
  • Any digits after these significant digits are lost, leading to a loss of precision.
• See Valid Constant Expressions for an example.

Single Precision Floating Point Value

• REAL is the default precision for floating points: such expressions do not require a prefix.
• Important: REAL is restrictive, but because it is the default, it is recommended to explicitly declare your real constants with the LREAL# prefix.
• Real constant expressions must be valid numbers, must include a dot (.).
• If you need to enter a real expression having an integer value, add .0 (dot zero) at the end of the number.
• You can use F or E separators for specifying the exponent in case of a scientific representation.
• REAL constants are limited to 6-7 digits of accuracy.
  • Any digits after these significant digits are lost, leading to a loss of precision.
• See Valid Constant Expressions for an example.

Small (8-bit) Integer

• Small integer constant expressions are valid integer values (between -128 and +127).
• Must be prefixed with SINT#.
• All integer expressions having no prefix are considered DINT integers.
• See Valid Constant Expressions for an example.

Character String

• String expressions must be written between single quote marks ('  ').
• The length of the string cannot exceed 255 characters.
• See Valid Constant Expressions for an example.
• Use these sequences to represent a special or not-printable character within a string:

Time of Day

• Time-constant expressions represent durations that must be less than 24 hours.
• Expressions must be prefixed by either T# or TIME#.
• They are expressed as a number of:
  • hours followed by h
  • minutes followed by m
  • seconds followed by s
  • milliseconds followed by ms
    
  • The order of units (hour, minutes, seconds, milliseconds) must be respected.
    • Blank characters are not allowed in the time expression.
    • There must be at least one valid unit letter in the expression.
    • See Valid Constant Expressions for an example.

Unsigned 32-bit Integer

• Unsigned 32-bit integer constant expressions are valid integer values (between 0 and 4294967295).
• Must be prefixed with UDINT#.
• All integer expressions having no prefix are considered DINT integers.

Unsigned 16-bit Integer

• Unsigned 16-bit integer constant expressions are valid integer values (between 0 and +65535).
• Must be prefixed with UINT#.
• All integer expressions having no prefix are considered DINT integers.

Unsigned Long Unsigned (64-bit) Integer

• Unsigned 64-bit integer constant expressions are valid integer values.
• All integer expressions having no prefix are considered DINT integers.

Character string.

Character string with a quote inside (I'm here).

Character string with two words separated by a tab.

Character string with two characters separated by a null character (ASCII code 0).

0 expressed as a REAL number.

1002 expressed as a REAL number in scientist format.

DINT integer in binary basis.

DINT integer in octal basis.

DINT integer in hexadecimal basis.

DINT (32-bit) integer.

FALSE Boolean expression.

16-bit integer.

Long (64 bit) integer having the value 1.

Double precision real number.

Small integer.

TIME value with some units missing.

Maximum TIME value.

Null TIME value.

Quote within a string with "$" mark omitted.

Basis prefix ("16#") omitted.

"LREAL#" prefix omitted for a double precision float.

0 and 1 cannot be used for Booleans.

Quotes omitted around a character string.