Intel 8XC196MD, 8XC196MH, 8XC196MC manual Controlling Access to the Otprom During Normal Operation

8XC196MC, MD, MH USER’S MANUAL

16.3.1.1Controlling Access to the OTPROM During Normal Operation

During normal operation, the lock bits in CCB0 control read and write accesses to the OTPROM. Table 16-2 describes the options. You can program the CCBs using any of the programming methods.

	Table 16-2. Memory Protection for Normal Operating Mode
Read Protect	Write Protect	Protection Status
LOC1 (CCR0.7)	LOC0 (CCR0.6)
1	1	No protection. Run-time programming is permitted, and the entire
		OTPROM array can be read.
1	0	Write protection only. Run-time programming is disabled, but the
		entire OTPROM array can be read.
		Read protection. Run-time programming is disabled. If program
0	1	execution is external, only the interrupt vectors and CCBs can be
		read. The security key is write protected.
		Read and write protection. Run-time programming is disabled. If
0	0	program execution is external, only the interrupt vectors and CCBs
		can be read.

Clearing CCB0.6 enables write protection. With write protection enabled, a write attempt causes the bus controller to cycle through the write sequence, but it does not enable VPP or write data to the OTPROM. This protects the entire OTPROM array from inadvertent or unauthorized pro- gramming.

Clearing CCB0.7 enables read protection and also write protects the security key to protect it from being overwritten. With read protection enabled, the bus controller will not read from pro- tected areas of OTPROM. An attempt to load the slave program counter with an external address causes the device to reset itself. Because the slave program counter can be as much as four bytes ahead of the CPU program counter, the bus controller might prevent code execution from the last four bytes of internal memory. The interrupt vectors and CCBs are not read protected because interrupts can occur even when executing from external memory.

16.3.1.2Controlling Access to the OTPROM During Programming Modes

For programming modes, three levels of protection are available:

•prohibit all programming

•prohibit all programming, but permit authorized ROM dumps

•permit authorized ROM dumps, auto programming, and slave programming

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