ISD91200 Series Technical Reference Manual
Release Date: Sep 16, 2019
- 45 -
Revision 2.4
Protected Register Lock Key Register (SYS_REGLCTL)
Certain critical system control registers are protected against inadvertent write operations which may
disturb chip operation. These system control registers are locked after power on reset until the user
specifically issues an unlock sequence to open the lock. The unlock sequence is to write to
SYS_REGLCTL the data 0x59, 0x16, 0x88. Any different sequence, data or a write to any other
address will abort the unlock sequence.
MDK provides the defined function UNLOCKREG(x); which will execute this sequence.
The status of the lock can be determined by reading SYS_REGLCTL bit0: “1” is unlocked, “0” is
locked. Once unlocked, user can update protected register values. To lock registers again, write any
data to SYS_REGLCTL.
This register is write accessible for writing key values and read accessible to determine REGLCTL
status.
Register
Offset
R/W
Description
Reset Value
SYS_REGLCTL
0x100 R/W
Register Lock Control
0x0000_0000
7
6
5
4
3
2
1
0
Reserved
REGLCTL
Table 5-11 Protected Register Lock Key Register (SYS_REGLCTL address 0x5000_0100).
Bits
Description
[31:1]
Reserved
Reserved.
[0]
REGLCTL
Protected Register Unlock Register
0 = Protected registers are locked. Any write to the target register is ignored.
1 = Protected registers are unlocked.
