MPC563XM Reference Manual, Rev. 1
Freescale Semiconductor
679
Preliminary—Subject to Change Without Notice
Figure 22-51. OPWFM with next period update
22.5.1.1.14
Output Pulse Width and Frequency Modulation Buffered (OPWFMB) Mode
This mode (MODE[0:6]=10110b0) provides waveforms with variable duty cycle and frequency. The
internal channel counter is automatically selected as the time base when this mode is selected. A1 register
indicates the duty cycle and B1 register the frequency. Both A1 and B1 registers are double buffered to
allow smooth signal generation when changing the registers values on the fly. 0% and 100% duty cycles
are supported.
At OPWFMB mode entry the output flip-flop is set to the value of the EDPOL bit in the EMIOSC[n]
register.
In order to provide smooth and consistent channel operation this mode differs substantially from the
OPWFM mode. The main differences reside in the A1 and B1 registers update, on the delay from the A1
match to the output pin transition and on the range of the internal counter values which starts from $1 up
to B1 register value.
If when entering OPWFMB mode coming out from GPIO mode the internal counter value is not within
that range then the B match will not occur causing the channel internal counter to wrap at the maximum
counter value which is $ff_ffff for a 24-bit counter. After the counter wrap occurs it returns to $1 and
resume normal OPWFMB mode operation. Thus in order to avoid the counter wrap condition make sure
its value is within the $1 to B1 register value range when the OPWFMB mode is entered.
When a match on comparator A occurs the output register is set to the value of EDPOL. When a match on
comparator B occurs the output register is set to the complement of EDPOL. B1 match also causes the
internal counter to transition to $1, thus restarting the counter cycle.
Only values greater than $1 are allowed to be written to B1 register. Loading values other than those leads
to unpredictable results.
describes the operation of the OPWFMB mode regarding output pin transitions and A1/B1
registers match events. Note that the output pin transition occurs when the A1 or B1 match signal is
$001000
$000000
internal counter
Time
Match A1
output flip-flop
A1 value
1
write to B2
$000200
B1 value
B2 value
2
$000900
Match B1
Match A1
$xxxxxx
$001000
$000200
Match B1
$000900
$001000
write to A2/B2
Match A1
Match B1
$000900
$000200
$001000
$000200
$001000
$000200
$000900
Notes: 1. EMIOSA[n] = A1
2. EMIOSB[n] = B2
A2 = A1according to OU[n] bit
B2 = B1according to OU[n] bit
MODE
[6]
= 1
Содержание MPC5632M
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