ZBasic System Library
214
ZBasic Microcontrollers
Type
Subroutine
Invocation
OutputCaptureEx(pin, intervals, count, flags)
OutputCaptureEx(pin, intervals, count, flags, repeatCount)
Parameter
Method
Type
Description
pin
ByVal
Byte
Specifies the waveform output pin.
intervals
ByRef
array of int16
The lengths of successive segments of the output waveform.
count
ByVal
any int
The number of entries in the intervals array (1-65535).
flags
ByVal
Byte
Configuration bits controlling the generation process.
repeatCount
ByVal
any int
The number of times to repeat the pattern (1-65535).
Discussion
This subroutine produces a series of precisely timed logic levels on the specified pin allowing you to
produce an arbitrary waveform. Each entry in the intervals array specifies a time interval, in units of
the I/O Timer clock period using the TimerSpeed 1 prescaler setting (i.e. 1/F_TS1, by default about
67.8ns for devices running at 14.7MHz), for each segment of the waveform. When called, the specified
pin will be made an output and will be set to its initial state (the complement of the least significant bit of
the flags parameter).
When waveform generation is begun, the specified pin will be changed to the opposite state for the
interval specified by the first intervals element, changed to the opposite state again for the interval
specified by the second intervals element, etc. for as many elements as specified. The final state of
the output pin depends on whether the count parameter is odd or even. If it is odd the final state will be
the complement of the least significant bit of the flags parameter; if it is even the final state will be the
same as the least significant bit of the flags parameter.
If the optional repeatCount parameter is not given a repeat count of 1 is assumed. If the repeat count
is 1 the intervals array should generally have an odd number of values. This allows the output to end
in the same state as it started. If the repeat count is greater than one the intervals array should
generally have an even number of values. This allows the output waveform to repeat at the same logic
levels. Also, when the waveform is repeated the last interval of the last cycle is omitted so that the output
ends up in the same state as it started.
The calling task will be suspended during the waveform generation process. If another task disables
interrupts, the accuracy of the generated waveform will suffer.
Due to processing overhead, the smallest pulse width that can be accommodated is equivalent to about
100 CPU cycles (6.8µS at 14.7MHz). This corresponds to a value of about 100 in the data array at the
default timer speed. If the system has a heavy interrupt load (e.g. serial channels 3-6 are open) the
minimum pulse width for reliable operation may be significantly larger. The maximum pulse width using
the default timer speed is about 4.4mS. If you need to generate longer pulse widths, you may set the
value of Register.TimerSpeed1 so that a slower clock rate is used.
To avoid unwanted logic transitions on the output pin during preparation for waveform generation, the
output pin should either be configured as an input or as an output in the desired starting state prior to the
call. If you configure it as an input you’ll probably need to employ a pullup or pulldown resistor on the pin
to guarantee the desired logic state prior to the commencement of waveform generation.
Although this subroutine can be invoked specifying a specific hardware OutputCapture pin (see the tables
in the Resource Usage sub-section Output Capture Timers) or a general I/O pin, the behavior when using
a general I/O pin may be slightly different than when using the specific hardware OutputCapture pin. The
hardware OutputCapture pin uses features of the hardware to toggle the I/O pin while for general I/O pins
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