Clocks and Power Control
MOTOROLA
MPC823e REFERENCE MANUAL
5-27
CLOCKS AND POWER
5
CONTROL
5.4.2.2 REGISTER LOCK.
The MPC823e registers that are powered by KAPWR can be
write-protected using the associated key register shown in Table 5-6. When the MPC823e
disconnects from the main power supply after it enters power-down mode, the value of these
registers is automatically preserved. You may lose data if you do not enter power-down
mode before disconnecting. To protect your data, lock the register by writing to the
associated key register. Once you lock a register, writes are ignored and a machine check
exception is generated.
Each of the registers in the keep-alive power region have a key register that can be in an
open or locked state. At power-on reset, all key registers are open, except for the key
real-time clock registers. Each key register has an associated address in the internal
memory map, as shown in Table 3-1. If you write 0x55CCAA33 to any of the key registers,
the associated register will be open
and if you write any other value it will be locked. For
example, writing a 0x55CCAA33 to the RTCK key register will allow you to access the RTC
register.
Table 5-6. Key Registers
MNEMONIC REGISTER NAME
TBSCRK Timebase Status and Control Register Key
TBREFFUK Timebase Reference Register Upper Key
TBREFFLK Timebase Reference Register Lower Key
TBK Timebase and Decrementer Register Key
RTCSCK Real-Time Clock Status and Control Register Key
RTCK Real-Time Clock Register Key
RTSECK Real-Time Alarm Seconds Key
RTCALK Real-Time Alarm Register Key
PISCRK Periodic Interrupt Status and Control Register Key
PITCK Periodic Interrupt Count Register Key
SCCRK System Clock Control Key
PLPRCRK PLL, Low Power and Reset Control Register Key
RSRK Reset Status Register Key
NOTE: Refer to
Section 3 Memory Map
for each register’s address.
Note:
A write of 0x55CCAA33 to any of the key registers in Table 5-6 will unlock the
associated SIU register and witing any other value will cause the associated
SIU register to be locked. Any other accesses to these key registers, inlcuding
reads, will cause the associated SIU register to be locked.
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