Freescale Semiconductor Demonstration Board for Freescale MC9S12XHY256 Microcontroller DEMO9S12XHY256 DEMO9S12XHY256 Manual De Usuario

Los códigos de productos

DEMO9S12XHY256

128 KByte Flash Module (S12XFTMR128K1V1)

MC9S12XHY-Family Reference Manual, Rev. 1.04

Freescale Semiconductor

629

19.3.2.2

Flash Security Register (FSEC)

The FSEC register holds all bits associated with the security of the MCU and Flash module.

All bits in the FSEC register are readable but not writable.

During the reset sequence, the FSEC register is loaded with the contents of the Flash security byte in the
Flash configuration field at global address 0x7F_FF0F located in P-Flash memory (see

Table 19-2

) as

indicated by reset condition F in

Figure 19-6

. If a double bit fault is detected while reading the P-Flash

phrase containing the Flash security byte during the reset sequence, all bits in the FSEC register will be
set to leave the Flash module in a secured state with backdoor key access disabled.

Offset Module Base + 0x0001

KEYEN[1:0]

RNV[5:2]

SEC[1:0]

Reset

= Unimplemented or Reserved

Figure 19-6. Flash Security Register (FSEC)

Table 19-7. FSEC Field Descriptions

Field

Description

7–6

KEYEN[1:0]

Backdoor Key Security Enable Bits — The KEYEN[1:0] bits define the enabling of backdoor key access to the
Flash module as shown in

Table 19-8

5–2

RNV[5:2}

Reserved Nonvolatile Bits — The RNV bits should remain in the erased state for future enhancements.

1–0

SEC[1:0]

Flash Security Bits — The SEC[1:0] bits define the security state of the MCU as shown in

Table 19-9

. If the

Flash module is unsecured using backdoor key access, the SEC bits are forced to 10.

Table 19-8. Flash KEYEN States

KEYEN[1:0]

Status of Backdoor Key Access

DISABLED

Preferred KEYEN state to disable backdoor key access.

ENABLED

DISABLED

Table 19-9. Flash Security States

SEC[1:0]

Status of Security

SECURED

UNSECURED

SECURED