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Chapter 22 Voltage Regulator (S12VREGL3V3V1)
MC9S12XE-Family Reference Manual Rev. 1.07
Freescale Semiconductor
841
22.4.7
Autonomous Periodical Interrupt (API)
Subblock API can generate periodical interrupts independent of the clock source of the MCU. To enable
the timer, the bit APIFE needs to be set.
The API timer is either clocked by a trimmable internal RC oscillator or the bus clock. Timer operation
will freeze when MCU clock source is selected and bus clock is turned off. See CRG specification for
details. The clock source can be selected with bit APICLK. APICLK can only be written when APIFE is
not set.
The APIR[15:0] bits determine the interrupt period. APIR[15:0] can only be written when APIFE is
cleared.AssoonasAPIFEisset,thetimerstartsrunningfortheperiodselectedbyAPIR[15:0]bits.When
the configured time has elapsed, the flag APIF is set. An interrupt, indicated by flag APIF = 1, is triggered
if interrupt enable bit APIE = 1. The timer is started automatically again after it has set APIF.
The procedure to change APICLK or APIR[15:0] is first to clear APIFE, then write to APICLK or
APIR[15:0], and afterwards set APIFE.
The API Trimming bits APITR[5:0] must be set so the minimum period equals 0.2 ms if stable frequency
is desired.
See
Table 22-7
for the trimming effect of APITR.
NOTE
The first period after enabling the counter by APIFE might be reduced by
APIstartupdelayt
sdel
.TheAPIinternalRCoscillatorclockisnotavailable
if VREG_3V3 is in Shutdown Mode.
It is possible to generate with the API a waveform at an external pin by enabling the API by setting APIFE
and enabling the external access with setting APIEA. By setting APIES the waveform can be selected. If
APIES is set, then at the external pin a clock is visible with 2 times the selected API Period (
Table 22-9
).
If APIES is not set, then at the external pin will be a high pulse at the end of every selected period with the
size of half of the min period (
Table 22-9
). See device level specification for connectivity.
22.4.8
Resets
This section describes how VREG_3V3 controls the reset of the MCU.The reset values of registers and
signals are provided in
Section 22.3, “Memory Map and Register Definition”
. Possible reset sources are
listed in
Table 22-10
.
Table 22-10. Reset Sources
Reset Source
Local Enable
Power-on reset
Always active
Low-voltage reset
Available only in Full Performance Mode