at89s52-33sc ATMEL Corporation, at89s52-33sc Datasheet - Page 20

• Manufacturer Part Number: at89s52-33sc
• Description: At89s52 , 8-bit Microcontroller With 8k Bytes In-system Programmable Flash
• Manufacturer: ATMEL Corporation

17. Program Memory Lock Bits
20
AT89S52
Figure 16-2. External Clock Drive Configuration
Table 16-1.
The AT89S52 has three lock bits that can be left unprogrammed (U) or can be programmed (P)
to obtain the additional features listed in
Table 17-1.
When lock bit 1 is programmed, the logic level at the EA pin is sampled and latched during reset.
If the device is powered up without a reset, the latch initializes to a random value and holds that
value until reset is activated. The latched value of EA must agree with the current logic level at
that pin in order for the device to function properly.
Mode
Idle
Idle
Power-down
Power-down
1
2
3
4
Program Lock Bits
LB1
U
P
P
P
Status of External Pins During Idle and Power-down Modes
Lock Bit Protection Modes
Program
Memory
Internal
External
Internal
External
LB2
U
U
P
P
LB3
U
U
U
P
OSCILLATOR
EXTERNAL
SIGNAL
ALE
NC
1
1
0
0
Protection Type
No program lock features
MOVC instructions executed from external program memory
are disabled from fetching code bytes from internal memory, EA
is sampled and latched on reset, and further programming of
the Flash memory is disabled
Same as mode 2, but verify is also disabled
Same as mode 3, but external execution is also disabled
Table
PSEN
1
1
0
0
17-1.
XTAL2
XTAL1
GND
PORT0
Float
Float
Data
Data
PORT1
Data
Data
Data
Data
Address
PORT2
Data
Data
Data
1919C–MICRO–3/05
PORT3
Data
Data
Data
Data