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UM10360_0
© NXP B.V. 2009. All rights reserved.
User manual
Rev. 00.06 — 5 June 2009
510 of 808
NXP Semiconductors
UM10360
Chapter 25: LPC17xx Motor Control PWM
Note:
In timer mode, the period of a channel’s modulated MCO outputs is determined by
its Limit register, and the pulse width at the start of the period is determined by its Match
register. If it suits your way of thinking, consider the Limit register to be the “Period register”
and the Match register to be the “Pulse Width register”.
Edge-aligned PWM without dead-time
In this mode the timer TC counts up from 0 to the value in the LIM register. As shown in
, the MCO state is “A passive” until the TC matches the Match register, at
which point it changes to “A active”. When the TC matches the Limit register, the MCO
state changes back to “A passive”, and the TC is reset and starts counting up again.
Center-aligned PWM without dead-time
In this mode the timer TC counts up from 0 to the value in the LIM register, then counts
back down to 0 and repeats. As shown in
, while the timer counts up, the
MCO state is “A passive” until the TC matches the Match register, at which point it
changes to “A active”. When the TC matches the Limit register it starts counting down.
When the TC matches the Match register on the way down, the MCO state changes back
to “A passive”.
Fig 120. Edge-aligned PWM waveform without dead time, POLA = 0
Fig 121. Center-aligned PWM waveform without dead time, POLA = 0
MAT
MAT
LIM
LIM
0
POLA = 0
timer reset
timer reset
MCOA
MCOB
active
active
passive
passive
passive
passive
active
active
MAT
MAT
LIM
LIM
0
0
POLA = 0
MCOA
MCOB
active
active
passive
passive
passive
passive
active
active