PXS20RM Datasheet, PDF (1188/1368 Pages) Freescale Semiconductor, Inc – PXS20 Microcontroller

Register Protection (REG_PROT)
Field
HLB
Table 40-4. GCR field descriptions
Description
Hard Lock Bit.
This register can not be cleared once it is set by software. It can only be cleared by a system reset.
UAA
1 All SLB bits are write protected and can not be modified.
0 All SLB bits are accessible and can be modified.
User Access Allowed.
1 The registers in the module under protection can be accessed in the mode defined for the module
registers without any additional restrictions.
0 The registers in the module under protection can only be written in supervisor mode. All write
accesses in non-supervisor mode are not executed and a transfer error is issued. This access
restriction is in addition to any access restrictions imposed by the protected IP module.
NOTE
The GCR[UAA] bit has no effect on the allowed access modes for the
registers in the REG_PROT module.
40.4 Functional description
40.4.1 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)
The list of protected modules and registers is shown in Section 40.6, PXS20 registers under protection.
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.
40.4.2 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.
40-6
PXS20 Microcontroller Reference Manual, Rev. 1
Freescale Semiconductor