TMS320F2812 PWM输出强制低无法实现

我参照手册TMS320x281x Event Manager (EV) Reference Guide.pdf 102中以下这段文字：

The compare action control registers (ACTRA and ACTRB) control the action
that takes place on each of the six compare output pins (PWMx, where x = 1−6
for ACTRA, and x = 7−12 for ACTRB) on a compare event, if the compare operation
is enabled by COMCONx[15]. ACTRA and ACTRB are doublebuffered.
The condition on which ACTRA and ACTRB is reloaded is defined
by bits in COMCONx. ACTRA and ACTRB also contain the SVRDIR, D2, D1,
and D0 bits needed for space vector PWM operation. The bit configuration of
ACTRA is described in Figure 5−9 and that of ACTRB is described in
Figure 5−10.

将COMCONA[15]使能，然后对ACTRA进行设置，发现Force High可以实现，Foce Low无法实现，查了整个文档，没有找到解释，

亟待解决，请大家帮忙。