do_pwm_transfer

Purpose:

Provide PWM on a Digital Out Bit.

Enter:

do_pwm_transfer <priority> <process_rate> [+c]

Where:

priority	Specify the system level task priority.
process_rate	Specify the rate at which update the PWM output.
+c	Optional. Specify this flag to indicate a critical task.

Example:

1. ctrl_specs output specification:
# Output type   DO PWM      PWM Period or a label  PWM enable label
#               label        containing period
DO      air_htr_bit         35[sec]              air_htr_enab

2. do_specs output specification
#chan  invert  up to 4 functional descriptions
0     0       $-$
#lbl  true_desc false_desc  true_event  false_event  hst  arm_dsply
air_htr_bit  ON       OFF            $-$           $-$       OFF     OFF
For this example, the DO bit ‘air_htr_bit’ will be used to provide a
PWM output that will have a base period of 35 seconds.  The duty cycle
of the PWM will be the value of the _CM control variable for the
associated control loop and the value of the LOGICAL_VARIABLE
‘air_htr_enab’ will be used to enable/disable the PWM output.
$-$$-$$-$$-$$-$$-$$-$$-$$-$$-$$-$$-$$-$$-$$-$$-$$-$$-$$-$$-$$-$$-$$-$$-$$-$$-$$-$-$$-$$-$
If the PWM is specified via do_specs, then the format of the specification is:
#chan  invert
0     0        PWM     period     DC_label  [enable_label]
#label   true_desc  false_desc  true_event  false_event  hst  arm_dsply
water_htr   ON         OFF          $-$           $-$        OFF      OFF
where:
PWM          = Is a new function code that indicates this bit will be used as a PWM Output bit. NOTE: If the PWM is provided
by the Control task, the PWM function code should not be specified for the DO bit.
period = A label whose value will be used as the base period of the PWM output. If the label does not exist it will be created. A numeric
value may be specified. For this case, the value must also contain the time units, e.g. 30[sec].
DC_label     = is the label of a REAL_VARIABLE that will contain desired Duty Cycle for the PWM output. If the label does not exist it will be created. A numeric value may be specified. For this case, the value must also contain units, eg. 30[%].
enable_label = The label of a LOGICAL_VARAIBLE that is used to disable/enable the PWM output. If the label does not exist it will
be created. This is an optional argument and if not present the PWM will always be active.
water_htr    = the label of DO bit that will provide the PWM
The remaining fields are the standard DO specs fields.
For example:
#chan  invert
0     0        PWM     htr_period     DC_water_htr  wtr_htr_enab
#label   true_desc  false_desc  true_event  false_event  hst  arm_dsply
water_htr   ON         OFF          $-$           $-$        OFF      OFF
For this example, the DO bit ‘water_htr’ will be used to provide a PWM output that will have a base period as defined in the REAL_VARIABLE
‘htr_period’.  The duty cycle for the PWM is defined in the REAL_VARIABLE ‘DC_water_htr’ and the value of LOGICAL_VARIABLE ‘wtr_htr_enab’ will be used to enable/disable the PWM output.

Notes:

This task is normally started in the go script. It is configured by either ctrl_specs or do_specs. If the control task is providing the control of the PWM duty cycle, the associated loop should have a ‘DO’ output type specified and the DO bit must be specified via do_specs. The syntax of the DO output type for the control specs is: DO <do_bit_label> <period> [enable_label] where:

<do_bit_label> is the label of the DO bit that provides the PWM output

<period> is a label or value for the base period of the PWM output

[enable_label] is an optional label for a variable to enable or disable the PWM output

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