Datasheet

PIC18F2331/2431/4331/4431
DS39616D-page 196 2010 Microchip Technology Inc.
18.10.3 OUTPUT OVERRIDE EXAMPLES
Figure 18-21 shows an example of a waveform that
might be generated using the PWM output override
feature. The figure shows a six-step commutation
sequence for a BLDC motor. The motor is driven
through a 3-phase inverter as shown in Figure 18-16.
When the appropriate rotor position is detected, the
PWM outputs are switched to the next commutation
state in the sequence. In this example, the PWM out-
puts are driven to specific logic states. The OVDCOND
and OVDCONS register values used to generate the
signals in Figure 18-21 are given in Tab l e 1 8-4.
The PWM Duty Cycle registers may be used in con-
junction with the OVDCOND and OVDCONS registers.
The Duty Cycle registers control the average voltage
across the load and the OVDCOND and OVDCONS
registers control the commutation sequence.
Figure 18-22 shows the waveforms, while Tab l e 1 8-4
and Table 18-5 show the OVDCOND and OVDCONS
register values used to generate the signals.
REGISTER 18-6: OVDCOND: OUTPUT OVERRIDE CONTROL REGISTER
R/W-1 R/W-1 R/W-1 R/W-1 R/W-1 R/W-1 R/W-1 R/W-1
POVD7
(1)
POVD6
(1)
POVD5 POVD4 POVD3 POVD2 POVD1 POVD0
bit 7 bit 0
Legend:
R = Readable bit W = Writable bit U = Unimplemented bit, read as ‘0’
-n = Value at POR ‘1’ = Bit is set ‘0’ = Bit is cleared x = Bit is unknown
bit 7-0 POVD<7:0>: PWM Output Override bits
1 = Output on PWM I/O pin is controlled by the value in the Duty Cycle register and the PWM time base
0 = Output on PWM I/O pin is controlled by the value in the corresponding POUT bit
Note 1: Unimplemented in PIC18F2331/2431 devices; maintain these bits clear.
REGISTER 18-7: OVDCONS: OUTPUT STATE REGISTER
(1,2)
R/W-0 R/W-0 R/W-0 R/W-0 R/W-0 R/W-0 R/W-0 R/W-0
POUT7
(1)
POUT6
(1)
POUT5 POUT4 POUT3 POUT2 POUT1 POUT0
bit 7 bit 0
Legend:
R = Readable bit W = Writable bit U = Unimplemented bit, read as ‘0’
-n = Value at POR ‘1’ = Bit is set ‘0’ = Bit is cleared x = Bit is unknown
bit 7-0 POUT<7:0>: PWM Manual Output bits
1 = Output on PWM I/O pin is active when the corresponding PWM output override bit is cleared
0 = Output on PWM I/O pin is inactive when the corresponding PWM output override bit is cleared
Note 1: Unimplemented in PIC18F2331/2431 devices; maintain these bits clear.
2: With PWMs configured in Complementary mode, the output of even numbered PWM (PM0,2,4) will be
complementary of the output of odd PWM (PWM1,3,5), irrespective of the POUT bit setting.