Analog Devices ADSP-SC58 Series Hardware Reference Manual page 948

The low-side output remains off, as in the case without crossover. The difference in cross-over is that the high-side
output changes character and becomes like the low-side. What actually occurs is that the low-side duty cycle is sent
to the high-side output pins, and the high-side duty cycle is sent to the low side pins. Because the
PWM_ACTL.DISLO bit =1, the low-side pin remains off (see
The XOVR and DISHI/DISLO Functionality figure shows this example. In case 1, PWM_ACTL.XOVR =0; and in
case 2, PWM_ACTL.XOVR =1.
Figure 19-18: XOVR and DISHI/DISLO Functionality
Brushless DC Motor (Electronically Commutated Motor) Control
In the control of an electronically commutated motor (ECM), only two inverter legs are switched at any time. Of-
ten, the high-side device in one leg must be switched on at the same time as the low-side driver in a second leg. It is
possible to turn on the high-side switch of phase A and the low-side switch of phase B at the same time by:
• Programming identical values for the duty cycles for two PWM channels (for example,
PWM_CH1), and
• Setting the PWM_BCTL.XOVR bit to crossover the BH and BL pair of PWM signals
To control ECM, normally the third inverter leg (phase C in this example) is disabled for a number of PWM cycles.
To implement this function, both the PWM_CH and PWM_CL outputs are disabled by setting the
PWM_CCTL.DISHI and PWM_CCTL.DISLO bits.
In normal ECM operation, each inverter leg is disabled for certain time periods so that the PWM channel registers
change based on the position of the rotor shaft (motor commutation).
ADSP-SC58x/ADSP-2158x SHARC+ Processor Hardware Reference
DT DT
PWM_AH
PWM_AL
PWM_AH
PWM_AL
50% DUTY CYCLE
Output Disable and Cross-Over Modes
Output Control Feature
CASE 1
PWM_AH0 = 0
MODELSCHx = 0
XOVER = 0
POLHI = 1
DISLO = 1
CASE 2
PWM_AH0 = 0
MODELSCHx = 0
XOVER = 1
POLHI = 1
DISLO = 1
Precedence).
PWM_CH0 =
19–27