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ZPLC Standard Library Reference

ZPLC provides a complete suite of standard function blocks (FBs) and functions compliant with IEC 61131-3. These are available across all editors (ST, IL, LD, FBD, SFC).

Below is the exhaustive reference to every standard function available in the ZPLC runtime.

1. Timers​

TON (On-Delay Timer)​

Delays a rising edge. The output Q goes TRUE only after IN has been TRUE for the duration of PT.

  • Inputs:
    • IN (BOOL): Trigger condition.
    • PT (TIME): Preset Time (duration to wait).
  • Outputs:
    • Q (BOOL): High if IN has been continuously high for PT.
    • ET (TIME): Elapsed Time since IN went high.

TOF (Off-Delay Timer)​

Preserves a high state for a duration after a falling edge. Q follows IN to TRUE immediately, but delays going FALSE until PT has elapsed.

  • Inputs:
    • IN (BOOL): Trigger condition.
    • PT (TIME): Preset Time (duration to keep high).
  • Outputs:
    • Q (BOOL): True while IN is true, plus PT duration after IN goes false.
    • ET (TIME): Elapsed Time since IN went low.

TP (Pulse Timer)​

Generates a pulse of fixed duration regardless of how long the input stays high.

  • Inputs:
    • IN (BOOL): Trigger condition (rising edge starts the pulse).
    • PT (TIME): Preset Time (pulse width).
  • Outputs:
    • Q (BOOL): Pulses true for exactly PT duration upon IN rising edge.
    • ET (TIME): Elapsed Time since pulse started.

2. Counters​

CTU (Count Up)​

Increments a value on every rising edge of the input.

  • Inputs:
    • CU (BOOL): Count up trigger (rising edge).
    • R (BOOL): Reset input; when TRUE, CV resets to 0.
    • PV (INT): Preset Value (target).
  • Outputs:
    • Q (BOOL): TRUE if CV >= PV.
    • CV (INT): Current counter value.

CTD (Count Down)​

Decrements a value on every rising edge of the input.

  • Inputs:
    • CD (BOOL): Count down trigger (rising edge).
    • LD (BOOL): Load input; when TRUE, CV is set to PV.
    • PV (INT): Preset Value (initial value).
  • Outputs:
    • Q (BOOL): TRUE if CV <= 0.
    • CV (INT): Current counter value.

CTUD (Count Up/Down)​

Combines the features of CTU and CTD.

  • Inputs:
    • CU (BOOL): Count up trigger.
    • CD (BOOL): Count down trigger.
    • R (BOOL): Reset to 0.
    • LD (BOOL): Load PV to CV.
    • PV (INT): Preset value.
  • Outputs:
    • QU (BOOL): TRUE if CV >= PV.
    • QD (BOOL): TRUE if CV <= 0.
    • CV (INT): Current counter value.

3. Bistable (Flip-Flop) Elements​

RS (Reset-Dominant Flip-Flop)​

  • Inputs: S (BOOL, Set), R1 (BOOL, Reset).
  • Outputs: Q1 (BOOL).
  • Behavior: Latches Q1 to TRUE when S is TRUE. Resets Q1 to FALSE when R1 is TRUE. If both S and R1 are TRUE, the output is FALSE (Reset wins).

SR (Set-Dominant Flip-Flop)​

  • Inputs: S1 (BOOL, Set), R (BOOL, Reset).
  • Outputs: Q1 (BOOL).
  • Behavior: Latches Q1 to TRUE when S1 is TRUE. Resets Q1 to FALSE when R is TRUE. If both S1 and R are TRUE, the output is TRUE (Set wins).

4. Edge Detection​

R_TRIG (Rising Edge Detector)​

  • Inputs: CLK (BOOL).
  • Outputs: Q (BOOL).
  • Behavior: Q is TRUE for exactly one execution cycle when CLK transitions from FALSE to TRUE.

F_TRIG (Falling Edge Detector)​

  • Inputs: CLK (BOOL).
  • Outputs: Q (BOOL).
  • Behavior: Q is TRUE for exactly one execution cycle when CLK transitions from TRUE to FALSE.

5. Math Functions​

Arithmetic Operators​

  • ADD(IN1, IN2): Returns IN1 + IN2. Supports ANY_NUM (INT, REAL).
  • SUB(IN1, IN2): Returns IN1 - IN2. Supports ANY_NUM.
  • MUL(IN1, IN2): Returns IN1 * IN2. Supports ANY_NUM.
  • DIV(IN1, IN2): Returns IN1 / IN2. Supports ANY_NUM.
  • MOD(IN1, IN2): Returns the integer remainder of IN1 / IN2. Supports ANY_INT.

Advanced Math​

ABS​

Calculates the absolute value.

  • Inputs: IN (ANY_NUM).
  • Outputs: (ANY_NUM) Absolute value of IN.

SQRT​

Calculates the square root of a number.

  • Inputs: IN (REAL).
  • Outputs: (REAL) Square root of IN.

SIN / COS / TAN​

Standard trigonometric functions (evaluated in radians).

  • Inputs: IN (REAL).
  • Outputs: (REAL) Sine, Cosine, or Tangent of IN.

6. Selection Functions​

MAX​

Returns the maximum of two values.

  • Inputs: IN1 (ANY_NUM), IN2 (ANY_NUM).
  • Outputs: (ANY_NUM) The larger of the two inputs.

MIN​

Returns the minimum of two values.

  • Inputs: IN1 (ANY_NUM), IN2 (ANY_NUM).
  • Outputs: (ANY_NUM) The smaller of the two inputs.

LIMIT​

Constrains a value within a specified range.

  • Inputs: MN (ANY_NUM, minimum), IN (ANY_NUM, input), MX (ANY_NUM, maximum).
  • Outputs: (ANY_NUM) Returns MN if IN < MN, returns MX if IN > MX, otherwise returns IN.

SEL​

Selects one of two values based on a boolean condition.

  • Inputs: G (BOOL, condition), IN0 (ANY, returned if G is FALSE), IN1 (ANY, returned if G is TRUE).
  • Outputs: (ANY) IN0 or IN1.

MUX​

Multiplexer. Selects one of N inputs based on an integer index.

  • Inputs: K (INT, selector index), IN0, IN1, ... (ANY).
  • Outputs: (ANY) Returns INk.

7. Bitwise Functions​

Logical Operators​

  • AND(IN1, IN2): Bitwise AND. Supports ANY_BIT (BYTE, WORD, DWORD).
  • OR(IN1, IN2): Bitwise OR. Supports ANY_BIT.
  • XOR(IN1, IN2): Bitwise Exclusive OR. Supports ANY_BIT.
  • NOT(IN): Bitwise Inversion. Supports ANY_BIT.

Shifting and Rotating​

SHL​

Shift Left mathematically multiplies by 2 for each shifted bit.

  • Inputs: IN (ANY_BIT), N (INT, number of bits to shift).
  • Outputs: (ANY_BIT) IN shifted left. Rightmost bits filled with 0.

SHR​

Shift Right mathematically divides by 2 for each shifted bit.

  • Inputs: IN (ANY_BIT), N (INT, number of bits to shift).
  • Outputs: (ANY_BIT) IN shifted right. Leftmost bits filled with 0.

ROL​

Rotate Left. Shift bits out of the left side re-enter on the right side.

  • Inputs: IN (ANY_BIT), N (INT).
  • Outputs: (ANY_BIT) Rotated value.

ROR​

Rotate Right. Shift bits out of the right side re-enter on the left side.

  • Inputs: IN (ANY_BIT), N (INT).
  • Outputs: (ANY_BIT) Rotated value.

8. String Functions​

ZPLC strings use bounded buffers (STRING[80]) with built-in overflow protection. Memory holds current length and maximum capacity.

  • LEN(s): Returns INT representing current character count of string s.
  • CONCAT(s1, s2): Appends s2 to s1 (modifies s1).
  • COPY(src, dst): Copies src string into dst.
  • CLEAR(s): Empties string s to 0 length.
  • LEFT(s, n): Modifies s to keep only the leftmost n characters.
  • RIGHT(s, n): Modifies s to keep only the rightmost n characters.
  • MID(s, pos, n): Modifies s to keep n characters starting at 1-based index pos.
  • FIND(s1, s2): Returns INT position (1-based) of s2 within s1, or 0 if not found.
  • INSERT(s1, s2, pos): Inserts s2 into s1 starting at index pos.
  • DELETE(s, pos, n): Removes n characters from s starting at index pos.
  • REPLACE(s1, s2, pos, n): Overwrites n characters in s1 starting at index pos using s2.
  • STRCMP(s1, s2): Lexicographical comparison. Returns INT (-1 if s1 < s2, 0 if s1 == s2, 1 if s1 > s2).

Note: You can also use standard = and < > operators directly on STRING variables to compare them for equality.

9. Type Conversions​

Use type conversion functions to safely move payloads between memory classes.

  • REAL_TO_INT(IN) / INT_TO_REAL(IN): Input INT or REAL, outputs corresponding conversion.
  • BOOL_TO_INT(IN) / INT_TO_BOOL(IN): TRUE becomes 1; FALSE becomes 0.
  • TIME_TO_DINT(IN) / DINT_TO_TIME(IN): Conversion between milliseconds integer and IEC TIME definitions.

10. System Functions​

UPTIME​

Returns the millisecond representation of the hardware/processor uptime.

  • Inputs: None.
  • Outputs: (UDINT / TIME) Uptime in milliseconds.

CYCLE_TIME​

Retrieves the execution time taken for the previous complete PLC scheduling scan.

  • Inputs: None.
  • Outputs: (UDINT / TIME) Last cycle duration in milliseconds. useful for profiling cyclic logic.

WATCHDOG_RESET​

Forces a clear on the hardware/software task watchdog. Use internally inside extended loops.

  • Inputs: None.
  • Outputs: (BOOL) TRUE if successful.