mpc823rg Freescale Semiconductor, Inc, mpc823rg Datasheet - Page 126

• Manufacturer Part Number: mpc823rg
• Description: Mpc823 Powerquicc Integrated Communications Processor For Portable Systems
• Manufacturer: Freescale Semiconductor, Inc

5.4.2.2 REGISTER LOCK. The MPC823 registers that are powered by KAPWR can be
write-protected using the associated key register shown in Table 5-6. When the MPC823
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.
NOTE: Refer to Section 3 Memory Map for each register’s address.
MNEMONIC
TBREFFUK
TBREFFLK
PLPRCRK
RTCSCK
TBSCRK
RTSECK
RTCALK
PISCRK
SCCRK
PITCK
RSRK
RTCK
TBK
Note: A write of 0x55CCAA33 to any of the key registers in Table 5-6 will unlock the
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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.
For More Information On This Product,
Timebase Status and Control Register Key
Timebase Reference Register Upper Key
Timebase Reference Register Lower Key
Timebase and Decrementer Register Key
Real-Time Clock Status and Control Register Key
Real-Time Clock Register Key
Real-Time Alarm Seconds Key
Real-Time Alarm Register Key
Periodic Interrupt Status and Control Register Key
Periodic Interrupt Count Register Key
System Clock Control Key
PLL, Low Power and Reset Control Register Key
Reset Status Register Key
MPC823 REFERENCE MANUAL
Table 5-6. Key Registers
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REGISTER NAME
Clocks and Power Control
5-27