NEC µPD72257 Preliminary User's Manual page 118

Chapter 4
4.7.3.10
Access
Address
Initial Value
31 30 29 28
15 14 13 12
Bit Bit name
SYSPROTECT
31 to 0
[31:0]
118
SYSPROTECT - System control write protection register
This register disables the System Controller registers write protection for a single
write access, hence protecting the System Controller registers against
unintentional write accesses.
Before writing to any System Controller register SYSPROTECT must be written
with 0000 00A5 . After that only one write access to the System Controller
H
address range is allowed.
Reading of SYSPROTECT returns an undefined value.
After any reset the write protection is enabled.
This register can be written in 32-bit units.
<SysC_Base> + 2C
H
none
27 26 25 24
SYSPROTECT[31:16]
11 10 9 8
SYSPROTECT[15:0]
Function
0000 00A5 must be written to SYSPROTECT[31:0] for deactivating the write protection
H
of all System Controller registers for the next write access to all System Controller
registers.
Preliminary User's Manual S19203EE1V3UM00
23 22 21 20
W
7 6 5 4
W
System Controller
19 18 17 16
3 2 1 0