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MPC555
/
MPC556
MODULAR INPUT/OUTPUT SUBSYSTEM (MIOS1)
MOTOROLA
USER’S MANUAL
Rev. 15 October 2000
15-25
15.12 MIOS Pulse Width Modulation Submodule (MPWMSM)
The purpose of the MIOS pulse width modulation submodule (MPWMSM) is to create
a variable pulse width output signal at a wide range of frequencies, independent of oth-
er MIOS1 output signals. The MPWMSM includes its own 8-bit prescaler and counter
and, thus, does not use the MIOS1 16-bit counter buses.
The MPWMSM pulse width can vary from 0.0% to 100.0%, with up to 16 bits of reso-
lution. The finest output resolution is the MCU IMB clock time divided by two (for a
F
SYS
of 40.0 MHz, the finest output pulse width resolution is 50 ns). With the full six-
teen bits of resolution and the overall prescaler divide ratio varying from divide-by-2 to
divide-by-4096, the period of the PWM output can range from 3.28 ms to 6.7 s (assum-
ing a f
SYS
of 40 MHz). By reducing the counting value, the output signal period can be
reduced. The period can be as fast as 205 µs (4.882 KHz) with twelve bits of resolu-
tion, as fast as 12.8 µs (78.125 KHz) with eight bits of resolution and as fast as 3.2 µs
(312.500 KHz) with six bits of resolution (still assuming a f
SYS
of 40 MHz and a first
stage prescaler divide-by-2 clock selection).
Refer to
for the MPWMSM relative I/O pin implementation.
Figure 15-6 MPWMSM Block Diagram
16-bit Down Counter
8- bit Prescaler
PS0 - PS7
Output
MIOB
Buffer
(NCOUNT)
= 0x0001
POL
Next Period Register
MPWMA
16-bit
Pulse Width Register
Next Pulse Width
Register MPWMB1
PWMB2
Output
Flip-Flop
PIN
TRSP
EN
Counter
Output
Pin
MPWMC
PWMB
Request Bus
<= Comparator
LOAD
FREN
Clock
FLAG
EN
DDR
Output
Logic
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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