Wait

Syntax:

Fixed Length Delay:

    Wait time units

Conditional Delay:

    Wait {While | Until} condition

Using a variable to specify a US delay with warning suppression:

    Wait timevalue US #OVERRIDEWARNING

Command Availability:

Available on all microcontrollers.

Explanation:

The Wait command causes the program to wait for either a specified amount of time (such as 1 second), or while/until a condition is true.

When using the fixed-length delay, a variety of units are available:

Unit Length of unit Delay range

us

1 microsecond

1 us - 65535 us

10us

10 microseconds

10 us - 2.55 ms

ms

1 millisecond

1 ms - 65535 ms

10ms

10 milliseconds

10 ms - 2.55 s

s

1 second

1 s - 255 s

m

1 minute

1 min - 255 min

h

1 hour

1 hour - 255 hours

At one stage, GCBASIC variables could not hold more than 255. The 10us and 10ms units were added as a way to work around this limit. There is now no such limit (Wait 1000 ms will work, for example), so these are not really needed. However, you may see them in some older examples or programs, and the 10us unit is sometimes the shortest delay that will work accurately.

Warning

PIC Devices Only
MS delays at clock frequencies below 28kHz are not supported and will silently fail.
US delays at clock frequencies below 250kHz are not supported and will silently fail.
US delays at lower clock frequencies are accurate ONLY when the value is divisible by 4. This is caused by the minimum ASM delay loop being a specific number of instructions.
US delays at lower clock frequencies, when not divisible by 4, will silently accept the value and produce incorrect delays. + Use #OVERRIDEWARNING to suppress the resulting warning. Delays at clock frequencies below 500kHz may be impacted by previous instructions; testing of actual delays is advised.

Example:

    'This code will wait until a button is pressed, then it will flash
    'a light every half a second and produce a 440 Hz tone.

    #chip 16F819, 8

    #define BUTTON PORTB.0
    #define SPEAKER PORTB.1
    #define LIGHT PORTB.2
    Dir BUTTON In
    Dir SPEAKER Out
    Dir LIGHT Out

    'Assumes Button switches on when pressed
    Wait Until BUTTON = 1          ' <<< the conditional form of Wait instruction
    Wait Until BUTTON = 0

    Do
      'Flash the light
      Set LIGHT On
      Wait 500 ms
      Set LIGHT Off

      'Produce the tone
      '440 Hz = 880 changes = tone on for 1.14 ms
      Repeat 440
        PulseOut SPEAKER, 1140 us
        Wait 114 10us 'Wait for 114 x 10 us (1.14 ms)
      End Repeat
    Loop

Key line: Wait Until BUTTON = 1 — blocks the program here, checking BUTTON repeatedly, until it reads 1; this is the conditional form of Wait, as opposed to the fixed-length Wait 500 ms used further down.

To suppress warnings when using US.

    dim timevariable as Word
    timevariable = 100 // 100 is an example value that assigns the variable.

    // Use #OVERRIDEWARNING to prevent warning messages
    wait timevariable US #OVERRIDEWARNING

See Also:

  • Conditions — the comparisons used in Wait While/Wait Until
  • Repeat — looping a fixed number of times, as combined with Wait above
  • PulseOut — timed pin pulses, often used alongside Wait
  • Pause — the older, milliseconds-only equivalent to a fixed-length Wait
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