MPC555
/
MPC556
MODULAR INPUT/OUTPUT SUBSYSTEM (MIOS1)
MOTOROLA
USER’S MANUAL
Rev. 15 October 2000
15-29
Table 15-23 MPWMSMSCR Bit Descriptions
Bit(s)
Name
Description
0
PIN
Pin input status. The PIN bit reflects the state present on the MPWMSM pin. The software can
thus monitor the signal on the pin.
The PIN bit is a read-only bit. Writing to the PIN bit has no effect.
1
DDR
Data direction register. The DDR bit indicates the direction for the pin when the PWM function
is not used (disable mode). Note that when the PWM function is used, the DDR bit has no effect.
lists the different uses for the polarity (POL) bit, the enable (EN) bit and the data
direction register (DDR) bit.
0 = Pin is an input.
1 = Pin is an output.
2
FREN
Freeze enable. This active high read/write control bit enables the MPWMSM to recognize the
freeze signal on the MIOB.
0 = MPWMSM not frozen even if the MIOB freeze line is active.
1 = MPWMSM frozen if the MIOB freeze line is active.
3
TRSP
Transparent mode. The TRSP bit indicates that the MPWMSM double buffers are transparent:
when the software writes to either the MPWMA or MPWMB1 register the value written is imme-
diately transferred to respectively the counter or register MPWMB2.
0 = Transparent mode de-activated.
1 = Transparent mode activated.
4
POL
Output polarity control. The POL bit works in conjunction with the EN bit and controls whether
the MPWMSM drives the pin with the true or the inverted value of the output flip-flop
lists the different uses for the polarity (POL) bit, the enable (EN) bit and the data
direction register (DDR) bit.
5
EN
Enable PWM signal generation. The EN bit defines whether the MPWMSM generates a PWM
signal or is used as an I/O channel:
lists the different uses for the polarity (POL) bit, the enable (EN) bit and the data
direction register (DDR) bit.
0 = PWM generation disabled (pin can be used as I/O).
1 = PWM generation enabled (pin is output only).
6:7
—
Reserved
8:15
CP
Clock Prescaler. This 8-bit read/write register stores the two’s complement of the desired mod-
ulus value for loading into the built-in 8-bit clock prescaler. The value loaded defines the divide
ratio for the signal that clocks the MPWMSM period counter.
gives the clock divide
ratio according to the CP values.
Table 15-24 PWMSM Output Pin Polarity Selection
Control Bits
Pin Direction
(I/O)
Pin State
Periodic
Edge
Variable
Edge
Optional
Interrupt On
POL
EN
DDR
0
0
0
I
Input
—
—
—
0
0
1
O
Always Low
—
—
—
0
1
—
O
High Pulse
Falling Edge
Rising Edge
Falling Edge
1
0
0
I
Input
—
—
—
1
0
1
O
Always High
—
—
—
1
1
—
O
Low Pulse
Rising Edge
Falling Edge
Rising Edge
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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