Z8FMC16100 Series Flash MCU
Product Specification
69
PWM Off State and Output Polarity
The default OFF state and the polarity of the PWM outputs are controlled by the PWMHI
and PWMLOoption bits. The PWMHIoption controls the OFF state and the polarity for the
PWM High outputs 0H, 1H, and 2H. The PWMLOoption controls the OFF state and the
polarity for the Low outputs 0L, 1L, and 2L.
The OFF state is the value programmed in the option bit. For example, programming
PWMHIto a 1 sets the OFF state of PWM0H, 1H, and 2H to a High logic value and the
active state a Low logic value. Conversely, programming PWMHIto a 0 causes the OFF
state to be a Low logic value. PWMLOis programmed in a similar manner.
The relative polarity of the PWM channel pairs is controlled by the POLx bits in the PWM
Control 1 Register (PWMCTL1). These bits do not affect the OFF state programmed by
the option bits. Setting these bits inverts the High and Low of the selected channels. The
relative channel polarity controls the order in which the signals of a given PWM pair tog-
gle. If a POLx bit is reset to zero, the High will first go active at the start of a PWM period.
Alternately., if the bit is set, the Low will go active first. A switching of the POLx bits is
synchronized with the PWM reload event (see below). In complementary mode, the
switch is additionally delayed until the end of the programmed deadband time.
PWM Channel Pair Enable
Following a Power-On Reset (POR), the PWM pins enter a high-impedance state. As the
internal reset proceeds, the PWM outputs are forced to the OFF state as determined by the
PWMHIand PWMLOOFF state option bits.
The PWM0EN, PWM1EN, and PWM2ENoption bits enable the PWM0, PWM1, and PWM2
output pairs, respectively. If a PWM channel pair is not enabled, it remains in a high-
impedance state after reset, and can be used as a general-purpose input.
PWM Reload Event
To prevent erroneous PWM pulse-widths and periods, registers that control the timing of
the output are buffered. Buffering causes all of the PWM compare values to update at the
same time. In other words, the registers that control the duty cycle and clock source pres-
caler only take effect upon a PWM reload event. A PWM reload event can be configured
to occur at the end of each PWM period, or only every 2, 4, or 8 PWM periods by setting
the RELFREQbits in the PWM Control 1 Register (PWMCTL1). The software must indi-
cate that all new values are ready by setting the READYbit in the PWM Control 0 Register
(PWMCTL0) to 1. After this READYbit has been set to 1, the buffered values take effect
at the next reload event.
PS024604-1005
P R E L I M I N A R Y
PWM Off State and Output Polarity
ZILOG [ ZILOG, INC. ]
