IEC61131 Common Elements

IEC 61131-3 is a standard in PLC computer programming languages. The five languages
* Ladder diagram (LD), graphical
* Function block diagram (FBD), graphical
* Structured text (ST), textual
* Instruction list (IL), textual
* Sequential function chart (SFC)to which this standard applies share common elements so different languages can be used in the same program.

Data Types

* Bit Strings - groups of on/off values
** BOOL - 1
** BYTE - 8
** WORD - 16
** DWORD - 32
** LWORD - 64

* INTEGER - whole numbers
** SINT - signed short (1 byte)
** INT - signed integer (2 byte)
** DINT - double integer (4 byte)
** LINT - long integer (8 byte)
** U - Unsigned - add a U to the type to make it unsigned integer.

* REAL - floating point IEC 559 (IEEE)
** REAL - (4 byte)
** LREAL - (8 byte)

*Time - duration for timers, processes.

* Date and Time of day:
** DATE - calendar date
** TIME_OF_DAY - clock time
** DATE_AND_TIME: time and date

* STRING - character strings surrounded by single quotes.
Escaped characters are preceded by a dollar sign.
($$ $' $L $N $P $R $T $xx) => ($ quote linefeed newline page(FF) return tab hex_value)
** WSTRING - holds multi-byte strings.

* Arrays - multiple values stored in the same variable.

* Sub Ranges - puts limits on value i.e., (4-20) for current

* Derived - type derived from one of the above types.
** TYPE - single type
** STRUCT - composite of several variables and types.

* Generic - groups of the above types:
** ANY
*** ANY_DERIVED
*** ANY_ELEMENTARY
*** ANY_MAGNITUDE
**** ANY_NUM - LREAL, REAL
**** ANY_INT - LINT, DINT, INT, SINT, ULINT, UDINT, UNIT, USINT
*** ANY_BIT - LWORD, DWORD, WORD, BYTE, BOOL
*** ANY_STRING - STRING, WSTRING
*** ANY_DATE - DATE, TOD, DT

Variables

Variable attributes: RETAIN, CONSTANT, AT
* Global
* Direct (local)
* I/O Mapping - Input, Output, I/O
* External
* Temporary

Configuration

* Resource - Like a CPU
* Tasks - Can be multiple per CPU.
* Programs - Can be executed once, on a timer, on an event.

Program Organization Units

* Functions
** Standard: ADD, SQRT, SIN, COS, GT, MIN, MAX, AND, OR, etc.
** Custom
* Function Blocks
** Standard:
** Custom - Libraries of functions can be supplied by a vendor or third party.
* Programs

Configuration, Resources, Tasks

* Configuration - processing resources, memory for IO, execution rates, number of tasks.