ldmicro.txt

用PIC單片機與AVR單片機製作PLC控制的階梯圖程序。

    down) the associated count on every rising edge of the rung input
    condition (i.e. what the rung input condition goes from false to
    true). The output condition from the counter is true if the counter
    variable is greater than or equal to 5, and false otherwise. The
    rung output condition may be true even if the input condition is
    false; it only depends on the counter variable. You can have CTU
    and CTD instructions with the same name, in order to increment and
    decrement the same counter. The RES instruction can reset a counter,
    or you can perform general variable operations on the count variable.


> CIRCULAR COUNTER             Cname
                           --{CTC 0:7}--

    A circular counter works like a normal CTU counter, except that
    after reaching its upper limit, it resets its counter variable
    back to 0. For example, the counter shown above would count 0, 1,
    2, 4, 5, 6, 7, 0, 1, 2, 3, 4, 5, 6, 7, 0, 2,.... This is useful in
    combination with conditional statements on the variable `Cname';
    you can use this like a sequencer. CTC counters clock on the rising
    edge of the rung input condition condition. This instruction must
    be the rightmost instruction in its rung.


> SHIFT REGISTER            {SHIFT REG   }
                           -{ reg0..3    }-

    A shift register is associated with a set of variables. For example,
    this shift register is associated with the variables `reg0', `reg1',
    `reg2', and `reg3'. The input to the shift register is `reg0'. On
    every rising edge of the rung-in condition, the shift register will
    shift right. That means that it assigns `reg3 := reg2', `reg2 :=
    reg1'. and `reg1 := reg0'. `reg0' is left unchanged. A large shift
    register can easily consume a lot of memory. This instruction must
    be the rightmost instruction in its rung.


> LOOK-UP TABLE             {dest :=     }
                           -{ LUT[i]     }-

    A look-up table is an ordered set of n values. When the rung-in
    condition is true, the integer variable `dest' is set equal to the
    entry in the lookup table corresponding to the integer variable
    `i'. The index starts from zero, so `i' must be between 0 and
    (n-1). The behaviour of this instruction is not defined if the
    index is outside this range. This instruction must be the rightmost
    instruction in its rung.


> PIECEWISE LINEAR TABLE    {yvar :=     }
                           -{ PWL[xvar]  }-

    This is a good way to approximate a complicated function or
    curve. It might, for example, be useful if you are trying to apply
    a calibration curve to convert a raw output voltage from a sensor
    into more convenient units.

    Assume that you are trying to approximate a function that converts
    an integer input variable, x, to an integer output variable, y. You
    know the function at several points; for example, you might know that

        f(0)   = 2
        f(5)   = 10
        f(10)  = 50
        f(100) = 100

    This means that the points

        (x0, y0)   = (  0,   2)
        (x1, y1)   = (  5,  10)
        (x2, y2)   = ( 10,  50)
        (x3, y3)   = (100, 100)

    lie on that curve. You can enter those 4 points into a table
    associated with the piecewise linear instruction. The piecewise linear
    instruction will look at the value of xvar, and set the value of
    yvar. It will set yvar in such a way that the piecewise linear curve
    will pass through all of the points that you give it; for example,
    if you set xvar = 10, then the instruction will set yvar = 50.

    If you give the instruction a value of xvar that lies between two
    of the values of x for which you have given it points, then the
    instruction will set yvar so that (xvar, yvar) lies on the straight
    line connecting those two points in the table.  For example, xvar =
    55 gives an output of yvar = 75. (The two points in the table are
    (10, 50) and (100, 100). 55 is half-way between 10 and 100, and 75
    is half-way between 50 and 100, so (55, 75) lies on the line that
    connects those two points.)

    The points must be specified in ascending order by x coordinate. It
    may not be possible to perform mathematical operations required for
    certain look-up tables using 16-bit integer math; if this is the
    case, then LDmicro will warn you. For example, this look up table
    will produce an error:

        (x0, y0)    = (  0,   0)
        (x1, y1)    = (300, 300)

    You can fix these errors by making the distance between points in
    the table smaller. For example, this table is equivalent to the one
    given above, and it does not produce an error:

        (x0, y0)    = (  0,   0)
        (x1, y1)    = (150, 150)
        (x2, y2)    = (300, 300)

    It should hardly ever be necessary to use more than five or six
    points. Adding more points makes your code larger and slower to
    execute. The behaviour if you pass a value of `xvar' greater than
    the greatest x coordinate in the table or less than the smallest x
    coordinate in the table is undefined. This instruction must be the
    rightmost instruction in its rung.


> A/D CONVERTER READ           Aname
                           --{READ ADC}--

    LDmicro can generate code to use the A/D converters built in to
    certain microcontrollers. If the input condition to this instruction
    is true, then a single sample from the A/D converter is acquired and
    stored in the variable `Aname'. This variable can subsequently be
    manipulated with general variable operations (less than, greater than,
    arithmetic, and so on). Assign a pin to the `Axxx' variable in the
    same way that you would assign a pin to a digital input or output,
    by double-clicking it in the list at the bottom of the screen. If
    the input condition to this rung is false then the variable `Aname'
    is left unchanged.

    For all currently-supported devices, 0 volts input corresponds to
    an ADC reading of 0, and an input equal to Vdd (the supply voltage)
    corresponds to an ADC reading of 1023. If you are using an AVR, then
    connect AREF to Vdd. You can use arithmetic operations to scale the
    reading to more convenient units afterwards, but remember that you
    are using integer math. In general not all pins will be available
    for use with the A/D converter. The software will not allow you to
    assign non-A/D pins to an analog input. This instruction must be
    the rightmost instruction in its rung.


> SET PWM DUTY CYCLE          duty_cycle
                           -{PWM 32.8 kHz}-

    LDmicro can generate code to use the PWM peripheral built in to
    certain microcontrollers. If the input condition to this instruction
    is true, then the duty cycle of the PWM peripheral is set to the
    value of the variable duty_cycle. The duty cycle must be a number
    between 0 and 100; 0 corresponds to always low, and 100 corresponds to
    always high. (If you are familiar with how the PWM peripheral works,
    then notice that that means that LDmicro automatically scales the
    duty cycle variable from percent to PWM clock periods.)

    You can specify the target PWM frequency, in Hz. The frequency that
    you specify might not be exactly achievable, depending on how it
    divides into the microcontroller's clock frequency. LDmicro will
    choose the closest achievable frequency; if the error is large then
    it will warn you. Faster speeds may sacrifice resolution.

    This instruction must be the rightmost instruction in its rung.
    The ladder logic runtime consumes one timer to measure the cycle
    time. That means that PWM is only available on microcontrollers
    with at least two suitable timers. PWM uses pin CCP2 (not CCP1)
    on PIC16 chips and OC2 (not OC1A) on AVRs.


> MAKE PERSISTENT            saved_var
                           --{PERSIST}--

    When the rung-in condition of this instruction is true, it causes the
    specified integer variable to be automatically saved to EEPROM. That
    means that its value will persist, even when the micro loses
    power. There is no need to explicitly save the variable to EEPROM;
    that will happen automatically, whenever the variable changes. The
    variable is automatically loaded from EEPROM after power-on reset. If
    a variable that changes frequently is made persistent, then the
    EEPROM in your micro may wear out very quickly, because it is only
    good for a limited (~100 000) number of writes. When the rung-in
    condition is false, nothing happens. This instruction must be the
    rightmost instruction in its rung.


> UART (SERIAL) RECEIVE          var
                           --{UART RECV}--

    LDmicro can generate code to use the UART built in to certain
    microcontrollers. On AVRs with multiple UARTs only UART1 (not
    UART0) is supported. Configure the baud rate using Settings -> MCU
    Parameters. Certain baud rates may not be achievable with certain
    crystal frequencies; LDmicro will warn you if this is the case.

    If the input condition to this instruction is false, then nothing
    happens. If the input condition is true then this instruction tries
    to receive a single character from the UART. If no character is read
    then the output condition is false. If a character is read then its
    ASCII value is stored in `var', and the output condition is true
    for a single PLC cycle.


> UART (SERIAL) SEND             var
                           --{UART SEND}--

    LDmicro can generate code to use the UARTs built in to certain
    microcontrollers. On AVRS with multiple UARTs only UART1 (not
    UART0) is supported. Configure the baud rate using Settings -> MCU
    Parameters. Certain baud rates may not be achievable with certain
    crystal frequencies; LDmicro will warn you if this is the case.

    If the input condition to this instruction is false, then nothing
    happens. If the input condition is true then this instruction writes
    a single character to the UART. The ASCII value of the character to
    send must previously have been stored in `var'. The output condition
    of the rung is true if the UART is busy (currently transmitting a
    character), and false otherwise.

    Remember that characters take some time to transmit. Check the output
    condition of this instruction to ensure that the first character has
    been transmitted before trying to send a second character, or use
    a timer to insert a delay between characters. You must only bring
    the input condition true (try to send a character) when the output
    condition is false (UART is not busy).

    Investigate the formatted string instruction (next) before using this
    instruction. The formatted string instruction is much easier to use,
    and it is almost certainly capable of doing what you want.


> FORMATTED STRING OVER UART                var
                                   -{"Pressure: \3\r\n"}-

    LDmicro can generate code to use the UARTs built in to certain
    microcontrollers. On AVRS with multiple UARTs only UART1 (not
    UART0) is supported. Configure the baud rate using Settings -> MCU
    Parameters. Certain baud rates may not be achievable with certain
    crystal frequencies; LDmicro will warn you if this is the case.

    When the rung-in condition for this instruction goes from false to
    true, it starts to send an entire string over the serial port. If
    the string contains the special sequence `\3', then that sequence
    will be replaced with the value of `var', which is automatically
    converted into a string. The variable will be formatted to take
    exactly 3 characters; for example, if `var' is equal to 35, then