Safety
MPC5606S Microcontroller Reference Manual, Rev. 7
116 Freescale Semiconductor
4.1.4 Functional description
4.1.4.1 General
This module provides a generic register (address) write-protection mechanism. The protection size can be:
• 32-bit (address = multiples of 4)
• 16-bit (address = multiples of 2)
• 8-bit (address = multiples of 1)
• Unprotected (address = multiples of 1)
This section gives examples for various protection configurations.
For all addresses that are protected there are SLBRn.SLBm bits that specify whether the address is locked.
When an address is locked it can only be read but not written in any mode (supervisor/normal). If an
address is unprotected, the corresponding SLBRn.SLBm bit is always 0b0, no matter what software is
writing to.
4.1.4.2 Change lock settings
To change the setting whether an address is locked or unlocked, the corresponding SLBRn.SLBm bit needs
to be changed. This can be done using the following methods:
• Modify the SLBRn.SLBm directly by writing to area #4
• Set the SLBRn.SLBm bit(s) by writing to the mirror module space (area #3)
Both methods are explained in the following sections.
4.1.4.2.1 Change lock settings directly via area #4
In memory area #4, the lock bits are located. They can be modified by writing to them. Each SLBRn.SLBm
bit has a mask bit SLBRn.WEm, which protects it from being modified. This masking makes
clear-modify-write operations unnecessary.
Figure 4-5 shows two modification examples. The left example shows a write access to the SLBRn register
specifying a mask value that allows modification of all SLBRn.SLBm bits. The example on the right
specifies a mask that only allows modification of the bits SLBRn.SLB[3:1].
Figure 4-5. Change lock settings directly via area #4
1
SLB3SLB2SLB1SLB0
SLBRn.WE[3:0]
SLBRn.SLB[3:0]
SLB3SLB2SLB1SLB0
SLBRn.SLB[3:0]
change allowed
to SLB3
write data
to SLB2to SLB1to SLB0
111
1SLBRn.WE[3:0]
to SLB3
write data
to SLB2to SLB1to SLB0
110
change allowed
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