Chapter 8 Pulse-Width Modulator (S12PWM8B8CV1)
MC9S12XDP512 Data Sheet, Rev. 2.17
380
Freescale Semiconductor
8.4
Functional Description
8.4.1
PWM Clock Select
There are four available clocks: clock A, clock B, clock SA (scaled A), and clock SB (scaled B). These
Clock A and B can be software selected to be 1, 1/2, 1/4, 1/8,..., 1/64, 1/128 times the bus clock. Clock SA
uses clock A as an input and divides it further with a reloadable counter. Similarly, clock SB uses clock B
as an input and divides it further with a reloadable counter. The rates available for clock SA are software
selectable to be clock A divided by 2, 4, 6, 8,..., or 512 in increments of divide by 2. Similar rates are
available for clock SB. Each PWM channel has the capability of selecting one of two clocks, either the
pre-scaled clock (clock A or B) or the scaled clock (clock SA or SB).
The block diagram in
Figure 8-18 shows the four different clocks and how the scaled clocks are created.
Table 8-9. PWMSDN Field Descriptions
Field
Description
7
PWMIF
PWM Interrupt Flag — Any change from passive to asserted (active) state or from active to passive state will
be agged by setting the PWMIF ag = 1. The ag is cleared by writing a logic 1 to it. Writing a 0 has no effect.
0 No change on PWM7IN input.
1 Change on PWM7IN input
6
PWMIE
PWM Interrupt Enable — If interrupt is enabled an interrupt to the CPU is asserted.
0 PWM interrupt is disabled.
1 PWM interrupt is enabled.
5
PWMRSTRT
PWM Restart — The PWM can only be restarted if the PWM channel input 7 is de-asserted. After writing a logic
1 to the PWMRSTRT bit (trigger event) the PWM channels start running after the corresponding counter passes
next “counter == 0” phase. Also, if the PWM7ENA bit is reset to 0, the PWM do not start before the counter
passes $00. The bit is always read as “0”.
4
PWMLVL
PWM Shutdown Output Level If active level as dened by the PWM7IN input, gets asserted all enabled PWM
channels are immediately driven to the level dened by PWMLVL.
0 PWM outputs are forced to 0
1 Outputs are forced to 1.
2
PWM7IN
PWM Channel 7 Input Status — This reects the current status of the PWM7 pin.
1
PWM7INL
PWM Shutdown Active Input Level for Channel 7 — If the emergency shutdown feature is enabled
(PWM7ENA = 1), this bit determines the active level of the PWM7channel.
0 Active level is low
1 Active level is high
0
PWM7ENA
PWM Emergency Shutdown Enable — If this bit is logic 1, the pin associated with channel 7 is forced to input
and the emergency shutdown feature is enabled. All the other bits in this register are meaningful only if
PWM7ENA = 1.
0 PWM emergency feature disabled.
1 PWM emergency feature is enabled.