Intel 8XC196NT User Manual page 368

These protection levels are provided by the PCCB0 lock bits, the CCB0 lock bits, and the internal
security key (Table 15-3). When entering programming modes, the reset sequence loads the
PCCBs into the chip configuration registers. It also loads CCB0 into internal RAM to provide an
additional level of security.
You can program the CCBs using any of the programming methods, but only slave programming
mode permits access to the PCCBs, and only slave and auto programming allow you to program
the internal security key.
Table 15-3. Memory Protection Options for Programming Modes
LOC1 LOC0
(CCR0.7) (CCR0.6)
PCCB CCB PCCB
1 1 1
1 X 0
X X X
1 0 1
0 X 0
If you want to prohibit all programming, clear both PCCB0 lock bits. If these bits are cleared,
they prevent the device from entering any programming mode.
If you want to prevent programming, but allow ROM dumps, leave the PCCB0 read-protection
bit (PCCB0.7) unprogrammed and clear the PCCB0 write-protection lock bit (PCCB0.6). To pro-
tect against unauthorized reads, program an internal security key. The ROM-dump mode com-
pares the internal security key location with an externally supplied security key regardless of the
CCB0 lock bits. If the security keys match, the routine continues; otherwise, the device enters an
endless internal loop.
If you want to allow slave and auto programming as well as ROM dumps, leave both PCCB0 lock
bits unprogrammed. To protect against unauthorized programming, clear the CCB0 lock bits and
program an internal security key. After the device enters either slave or auto programming mode,
the corresponding test ROM routine reads the CCB0 lock bits. If either CCB0 lock bit is enabled,
the routine compares the internal security key location with an externally supplied security key.
If the security keys match, the routine continues; otherwise, the device enters an endless internal
loop.
Security Key
Programmed
?
CCB
1 No No protection. All programming modes allowed.
All programming disabled. ROM-dump permitted with
X Yes
matching security key.
X Yes Serial programming disabled.
Serial programming disabled. Auto and slave
0 Yes
programming permitted with matching security key.
X X All programming unconditionally disabled.
PROGRAMMING THE NONVOLATILE MEMORY
Protection Status
15-5