MPC555
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MPC556
SYSTEM CONFIGURATION AND PROTECTION
MOTOROLA
USER’S MANUAL
Rev. 15 October 2000
6-33
6.13.4.6 Real-Time Clock Register (RTC)
The real-time clock register is a 32-bit read write register. It contains the current value
of the real-time clock. A write to the RTC resets the seconds timer to zero. This register
is locked after RESET. Unlocking is accomplished by writing 0x55CCAA33 to its as-
sociated key register. See
8.9.3.2 Keep Alive Power Registers Lock Mechanism
6.13.4.7 Real-Time Clock Alarm Register (RTCAL)
The RTCAL is a 32-bit read/write register. When the value of the RTC is equal to the
value programmed in the alarm register, a maskable interrupt is generated.
The alarm interrupt will be generated as soon as there is a match between the ALARM
field and the corresponding bits in the RTC. The resolution of the alarm is 1 sec. This
register is locked after RESET. Unlocking is accomplished by writing 0x55CCAA33 to
its associated key register. See
8.9.3.2 Keep Alive Power Registers Lock Mecha-
Table 6-17 RTCSC Bit Descriptions
Bit(s)
Name
Description
0:7
RTCIRQ
Real-time clock interrupt request. Thee bits determine the interrupt priority level of the RTC. Re-
fer to
for interrupt level encodings.
8
SEC
Once per second interrupt. This status bit is set every second. It should be cleared by the soft-
ware.
9
ALR
Alarm interrupt. This status bit is set when the value of the RTC equals the value programmed in
the alarm register.
10
—
Reserved
11
4M
Real-time clock source
0 = RTC assumes that it is driven by 20 MHz to generate the seconds pulse.
1 = RTC assumes that it is driven by 4 MHz
12
SIE
Second interrupt enable. If this bit is set, the RTC generates an interrupt when the SEC bit is set.
13
ALE
Alarm interrupt enable. If this bit is set, the RTC generates an interrupt when the ALR bit is set.
14
RTF
Real-time clock freeze. If this bit is set, the RTC stops while FREEZE is asserted.
15
RTE
Real-time clock enable
0 = RTC is disabled
1 = RTC is enabled
RTC
—Real-Time Clock Register
0x2F C224
MSB
0
LSB
31
RTC
RESET: UNCHANGED
RTCAL
— Real-Time Clock Alarm Register
0x2F C22C
MSB
0
LSB
31
ALARM
RESET: UNCHANGED
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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