Motorola MPC860 PowerQUICC, User Manual, Page: 285 / 1106

MOTOROLA Chapter 11. System Interface Unit 11-11
Part III. Configuration
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.
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
Table 11-6. Key Registers
Offset Name Size
System Integration Timers Keys
0x300 TBSCRKÑTimebase status and control register key 32 bits
0x304 TBREFAKÑTimebase reference register A key 32 bits
0x308 TBREFBKÑTimebase reference register B key 32 bits
0x30C TBKÑTimebase/decrementer register key 32 bits
0x310Ð31F Reserved 16 bytes
0x320 RTCSCKÑReal-time clock status and control register key 32 bits
0x324 RTCKÑReal-time clock register key 32 bits
0x328 RTSECKÑReal-time alarm seconds key 32 bits
0x32C RTCALKÑReal-time alarm register key 32 bits
0x330Ð33F Reserved 16 bytes
0x340 PISCRKÑPeriodic interrupt status and control register key 32 bits
0x344 PITCKÑPeriodic interrupt count register key 32 bits
0x348Ð37F Reserved 56 bytes
Clocks and Reset Keys
0x380 SCCRKÑSystem clock control key 32 bits
0x384 PLPRCRKÑPLL, low power and reset control register key 32 bits
0x388 RSRKÑReset status register key 32 bits
0x38CÐ7FF Reserved 1140 bytes