20. Lock Bits, Fuse Bits and Device Signature

20.1Lock Bits

ATtiny2313A/4313 provides the program and data memory lock bits listed in Table 20-1.

Table 20-1.	Lock Bit Byte
Lock Bit Byte		Bit No	Description	See	Default Value (1)
–		7	–		1 (unprogrammed)
–		6	–		1 (unprogrammed)
–		5	–		1 (unprogrammed)
–		4	–		1 (unprogrammed)
–		3	–		1 (unprogrammed)
–		2	–		1 (unprogrammed)
LB2		1	Lock bit	Below	1 (unprogrammed)
LB1		0			1 (unprogrammed)

Notes: 1. “1” means unprogrammed, “0” means programmed.

Lock bits can be left unprogrammed (“1”) or can be programmed (“0”) to obtain the additional features listed in Table 20-2.

Table 20-2.	Lock Bit Protection Modes.
Lock Bits (1)
LB2	LB1	Mode of Protection
1	1	No memory lock features enabled
		Further programming of Flash and EEPROM is disabled in parallel and serial
1	0	programming mode. Fuse bits are locked in both serial and parallel
		programming mode (2)
0	1	Reserved
		Further reading and programming of Flash and EEPROM is disabled in
0	0	parallel and serial programming mode. Fuse bits are locked in both serial and
		parallel programming mode (2)

Notes: 1. “1” means unprogrammed, “0” means programmed.

2. Program fuse bits before programming LB1 and LB2.

When programming the lock bits, the mode of protection can be increased, only. Writing the same, or lower, mode of protection automatically results in maximum protection.

Lock bits can be erased to “1” with the Chip Erase command, only.

The ATtiny2313A/4313 has no separate boot loader section. The SPM instruction is enabled for the whole Flash if the SELFPRGEN fuse is programmed (“0”), otherwise it is disabled.

178 ATtiny2313A/4313

8246B–AVR–09/11