Motorola MPC860 PowerQUICC User Manual page 285

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11.4.5 Register Lock Mechanism
If the MPC860 sets PLPRCR[LPM] = 11 before entering power-down mode, then the
registers of the SIU maintained by KAPWR are automatically protected. However, to
provide protection of the SIU registers maintained by KAPWR against uncontrolled
shutdown, a register locking mechanism is included. These registers can be write-protected
in a set of associated key registers.
The MPC860 key registers are shown in Table 11-6.
Offset
0x300
0x304
0x308
0x30C
0x310Ð31F Reserved
0x320
0x324
0x328
0x32C
0x330Ð33F Reserved
0x340
0x344
0x348Ð37F Reserved
0x380
0x384
0x388
0x38CÐ7FF Reserved
Each register in the keep-alive power region has a key register that can be in an open or
locked state. At power-on reset, all key registers are open, except for the real-time clock key
registers. Each key register has an associated address in the internal memory map, as shown
in Table 11-6. A write of 0x55CCAA33 to a key registers will unlock its associated SIU
register; any other access (including reads or writes of any other value) to a key register will
lock its associated SIU register. For example, writing a 0x55CCAA33 to the RTCK key
register allows the RTC register to be written. The key registers are write-only; a read of the
MOTOROLA
Table 11-6. Key Registers
System Integration Timers Keys
TBSCRKÑTimebase status and control register key
TBREFAKÑTimebase reference register A key
TBREFBKÑTimebase reference register B key
TBKÑTimebase/decrementer register key
RTCSCKÑReal-time clock status and control register key
RTCKÑReal-time clock register key
RTSECKÑReal-time alarm seconds key
RTCALKÑReal-time alarm register key
PISCRKÑPeriodic interrupt status and control register key
PITCKÑPeriodic interrupt count register key
Clocks and Reset Keys
SCCRKÑSystem clock control key
PLPRCRKÑPLL, low power and reset control register key
RSRKÑReset status register key
Chapter 11. System Interface Unit
Name
Part III. Configuration
Size
32 bits
32 bits
32 bits
32 bits
16 bytes
32 bits
32 bits
32 bits
32 bits
16 bytes
32 bits
32 bits
56 bytes
32 bits
32 bits
32 bits
1140 bytes
11-11

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