
Pulse-Width Modulator for Motor Control (PWMMC)
Fault Protection
MC68HC08MR4/MC68HC908MR8
Advance Information
MOTOROLA
Pulse-Width Modulator for Motor Control (PWMMC)
157
9.7.1 Fault Condition Input Pins
A logic high level on a fault pin disables the respective PWM(s)
determined by the bank and the disable mapping register. Each fault pin
incorporates a filter to assist in rejecting spurious faults. All of the
external fault pins are software-configurable to re-enable the PWMs
either with the fault pin (automatic mode) or with software (manual
mode). Each fault pin has an associated FMODE bit to control the PWM
re-enabling method. Automatic mode is selected by setting the FMODEx
bit in the fault control register. Manual mode is selected when FMODEx
is clear.
NOTE:
PORTC, when used as an input port, mirrors the state of the fault input
pins, as PORTC has the capability of being used as an output port.
When either pin of PORTC is set as an output, by setting its respective
PORTC data direction register bit, the respective fault pin logic is
disconnected from that pin and the fault input will be defaulted to normal
non-fault condition to facilitate the use of PORTC as an output pin and
not interfere with the PWM generator. To regain the fault capability for
the respective fault input pin, clear the PORTC data direction register bit
for that pin.
9.7.1.1 Fault Pin Filter
The two fault pins incorporate a filter to assist in determining a genuine
fault condition. After a fault pin has been logic low for one CPU cycle, a
rising edge (logic high) will be synchronously sampled once per CPU
cycle for two cycles. If both samples are detected logic high, the
corresponding FPIN bit and FFLAG bit will be set. The FPIN bit will
remain set until the corresponding fault pin is logic low and
synchronously sampled once in the following CPU cycle.
9.7.1.2 Automatic Mode
In automatic mode, the PWM(s) are disabled immediately once a filtered
fault condition is detected (logic high). The PWM(s) remain disabled until
the filtered fault condition is cleared (logic low) and a new PWM cycle
begins as shown in Figure 9-24. Clearing the corresponding FFLAGx
event bit will not enable the PWMs in automatic mode.