Modular Input/Output Subsystem (MIOS14)
MPC561/MPC563 Reference Manual, Rev. 1.2
17-50
Freescale Semiconductor
•
The value 0x0000 in the period register, causes the counter to act like a free running counter. This
condition creates a period of 65536 PWM clock periods.
•
The value 0x0001 in the period register will always cause a period match to occur and the counter
will never decrement below 0x0001. This condition is defined as a period of “1” PWM clock count.
The output flip-flop is always set unless MPWMPULR = 0x0000, when the output flip-flop is
always reset. Refer to
Section 17.10.3.5, “Duty Cycles (0% and 100%)
” for details about 0% and
100% duty cycles.
•
Writing value 0x0002 in the period register causes a period match to occur every two clock periods.
The counter decrements from 0x0002 to 0x0001, and then it is initialized back to 0x0002. This
condition is defined as a period of 2 clock counts. Note that the value 0x0002 loaded in the period
register and a value of 0x0001 in the pulse width register is the condition to obtain the maximum
possible output frequency for a given clock period.
The relationship between the output frequency obtained (F
PWMO
) and the MIOS14 CLOCK frequency
(f
SYS
), the MCPSM clock divide ratio (N
MCPSM
), the counter divide ratio (N
MPWMSM
) and the value
loaded in the counter (V
COUNTER
) is given by the following equation:
17.10.3.4 Pulse Width Registers
The pulse width section is composed of two 16-bit data registers (MPWMPULR1 and MPWMPULR2).
Only MPWMPULR1 is accessible by software. The software establishes the pulse width of the
MPWMSM output signal in MPWMPULR1. MPWMPULR2 is used as a double buffer of
MPWMPULR1.
When the MPWMSM is running in transparent mode, the pulse width value in MPWMPULR1 is
immediately transferred in MPWMPULR2 so that the new value takes effect immediately.
NOTE
When the MPWMSM is in disable mode, writing to MPWMPULR1 will
write automatically to MPWMPULR2.
When the MPWMSM is not running in double-buffered mode, the pulse width value in MPWMPULR1
can be changed at any time without affecting the current pulse width of the output signal. The new value
in MPWMPULR1 will be transferred to MPWMPULR2 only when the down-counter reaches the value of
0x0001.
When the counter first reaches the value in MPWMPULR2, the output flip-flop is set. The output is reset
when the counter reaches 0x0001. The pulse width match starts the width of the output signal, it does not
affect the counter. MPWMPULR1 is software readable and writable at any time. The MPWMSM does not
modify the content of MPWMPULR1.
The PWM output pulse width can be as wide as one period minus one MPWMSM clock count: (i.e.,
MPWMPULR2 = MPWMPERR — [one MPWMSM clock count]). At the other end of the pulse width
range, MPWMPULR2 can contain 0x0001 to create a pulse width of one PWM clock count.
f
PWMO
=
f
SYS
N
MCPSM
• N
MPWMSM
• V
COUNTER
Summary of Contents for MPC561
Page 84: ...MPC561 MPC563 Reference Manual Rev 1 2 lxxxiv Freescale Semiconductor...
Page 144: ...Signal Descriptions MPC561 MPC563 Reference Manual Rev 1 2 2 46 Freescale Semiconductor...
Page 206: ...Central Processing Unit MPC561 MPC563 Reference Manual Rev 1 2 3 62 Freescale Semiconductor...
Page 302: ...Reset MPC561 MPC563 Reference Manual Rev 1 2 7 14 Freescale Semiconductor...
Page 854: ...Time Processor Unit 3 MPC561 MPC563 Reference Manual Rev 1 2 19 24 Freescale Semiconductor...
Page 968: ...Development Support MPC561 MPC563 Reference Manual Rev 1 2 23 54 Freescale Semiconductor...
Page 1144: ...Internal Memory Map MPC561 MPC563 Reference Manual Rev 1 2 B 34 Freescale Semiconductor...
Page 1212: ...TPU3 ROM Functions MPC561 MPC563 Reference Manual Rev 1 2 D 60 Freescale Semiconductor...
Page 1216: ...Memory Access Timing MPC561 MPC563 Reference Manual Rev 1 2 E 4 Freescale Semiconductor...
