MPC555
/
MPC556
CLOCKS AND POWER CONTROL
MOTOROLA
USER’S MANUAL
Rev. 15 October 2000
8-25
illustrates the process of locking or unlocking a register powered by KAP-
WR.
Figure 8-12 Keep Alive Register Key State Diagram
8.10 VDDSRAM Supply Failure Detection
A special circuit for VDDSRAM supply failure detection is provided. In the case of sup-
ply failure detection, the dedicated sticky bits LVSRS in the VSRMCR register are as-
serted. Software can read or clear these bits. The user should enable the detector and
then clear these bits. If the user reads any of the LVSR bits as one, then a power failure
of VDDSRAM has occurred. The circuit is capable of detecting supply failure below 2.6
V. Also, enable/disable control bit for the VDDSRAM detector may be used to discon-
nect the circuit and save the detector power consumption.
8.11 Power Up/Down Sequencing
and
detail the power-up sequencing for MPC555 / MPC556
during normal operation. Note that for each of the conditions detailing the voltage re-
lationships the absolute bounds of the minimum and maximum voltage supply cannot
be violated, i.e. the value of VDDL cannot fall below 3.0 V or exceed 3.6 V and the
value of VDDH cannot fall below 4.5 V or exceed 5.5 V for normal operation. Further
information detailing the functionality of the VPP signal for flash program and erase is
outlined in
19.9.2 FLASH Program/Erase Voltage Conditioning
. Power consump-
tion during power up sequencing can not be specified prior to evaluation and charac-
SPR 22
Decrementer
See
3.9.5 Decrementer Register (DEC)
for bit descriptions.
0x2F C30C
Time Base and Decrementer Key (TBK)
SPR 268, 269,
284, 285,
Time Base
See
and
for bit de-
scriptions.
Table 8-8 KAPWR Registers and Key Registers (Continued)
KAPWR Register
Associated Key Register
Address or
SPR Number
Register
Address
Register
Open
Locked
Write to the Key 0x55CCAA33
Write to the key other value
Power On Reset
(Valid for RTC, RTSEC,
RTCAL and RTCSC)
(Valid for other registers)
Power On Reset
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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