NXP Semiconductors
FXTH87E
FXTH87E, Family of Tire Pressure Monitor Sensors
fBUS
PRDIV8
(Binary)
DIV5:DIV0
(Decimal)
fFCLK
Program/Erase Timing Pulse
(5 μs Min, 6.7 μs Max)
150 kHz
0
0
150 kHz
6.7 μs
6.9.2 FLASH options register (FOPT and NVOPT)
During reset, the contents of the nonvolatile location NVOPT are copied from FLASH into
FOPT. Bits 5 through 2 are not used and always read 0. This register may be read at any
time, but writes have no meaning or effect. To change the value in this register, erase
and reprogram the NVOPT location in FLASH memory as usual and then issue a new
MCU reset.
Table 17.ꢀFLASH options register (FOPT) (address $1821)
Bit
R
7
6
5
4
3
2
1
0
KEYEN
FNORED
0
0
0
0
SEC1
SEC0
W
Reset
This register is loaded from nonvolatile location NVOPT during reset.
= Reserved
Table 18.ꢀFOPT register field descriptions
Field
Description
Backdoor Key Mechanism Enable — When this bit is 0, the backdoor key mechanism cannot be used to
disengage security.
The backdoor key mechanism is accessible only from user (secured) firmware. BDM commands cannot
be used to write key comparison values that would unlock the backdoor key. For more detailed information
about the backdoor key mechanism, refer to Section 6.8 "Security".
7
KEYEN
0ꢀNo backdoor key access allowed
1ꢀIf user firmware writes an 8-byte value that matches the nonvolatile backdoor key (NVBACKKEY through
NVBACKKEY+7 in that order), security is temporarily disengaged until the next MCU reset
Vector Redirection Disable — When this bit is 1, then vector redirection is disabled.
0ꢀVector redirection enabled
6
FNORED
1ꢀVector redirection disabled
Security State Code — This 2-bit field determines the security state of the MCU as shown in Table 19.
When the MCU is secure, the contents of RAM and FLASH memory cannot be accessed by instructions
from any unsecured source including the BACKGROUND DEBUG interface. For more detailed information
about security, refer to Section 6.8 "Security". SEC[1:0] changes to 1 0 after successful backdoor key entry
or a successful blank check of FLASH.
1:0
SEC[1:0]
Table 19.ꢀSecurity states
SEC[1:0]
0 0
Description
secure
0 1
secure
1 0
unsecured
secure
1 1
FXTH87ERM
All information provided in this document is subject to legal disclaimers.
© NXP B.V. 2019. All rights reserved.
Reference manual
Rev. 5.0 — 4 February 2019
32 / 183
NXP [ NXP ]
