Modular Input/Output Subsystem (MIOS14)
MPC561/MPC563 Reference Manual, Rev. 1.2
17-74
Freescale Semiconductor
It is typical to use the pulse width modulation mode of the MDASM without interrupts, although an
interrupt can be enabled to occur on the leading edge. When the output is an unchanging repetitive
waveform, the MDASM continuously generates the signal without any software intervention. When the
software needs to change the pulse width, a new trailing edge time is written to the MDASM. The output
is changed on the next full pulse. When the software needs to change the output at a regular rate, such as
an acceleration curve, the leading edge interrupt gives the software one period time to update the new
trailing edge time.
Figure 17-46. MIOS14 Example: Pulse Width Modulation Output
17.13.5 MIOS14 Input Pulse Accumulation
Counting the number of pulses on an input signal is another capability of the MIOS14. Pulse accumulation
uses an MMCSM. Since the counters in the counter submodules are software accessible, pulse
accumulation does not require the use of an action submodule. The pulse accumulation can operate
continuously, interrupting only on binary overflow of the 16-bit counter. When an MMCSM is used, an
interrupt can instead be created when the pulse accumulation reaches a preprogrammed value. To do that,
the two’s complement of the value is put in the modulus register and the interrupt occurs when the counter
overflows.
16-bit Up-Counter
Submodule Bus
16-bit Compare B
Output
Flip-Flop
Output
Pin
16-bit Compare A
16-bit Register B2
16-bit Register A
Output
Compare
Interrupt
on
Bus
From
Prescaler
or Pin
Leading
16-bit Register B1
Edge
Modulus Register
Modulus
Control
Clock
Select
Load
Select
Two
16-bit
Counter
Buses
MIOS14 Double Action Submodule
in OCAB mode (MOD3 – MOD0 = 0b0101)
MIOS14 Modulus Counter Submodule
Summary of Contents for MPC561
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Page 206: ...Central Processing Unit MPC561 MPC563 Reference Manual Rev 1 2 3 62 Freescale Semiconductor...
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Page 1144: ...Internal Memory Map MPC561 MPC563 Reference Manual Rev 1 2 B 34 Freescale Semiconductor...
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