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AT89S52-24PU Datasheet(PDF) 20 Page - ATMEL Corporation

Part No. AT89S52-24PU
Description  8-bit Microcontroller with 8K Bytes In-System Programmable Flash
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Maker  ATMEL [ATMEL Corporation]
Homepage  http://www.atmel.com
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 20 page
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20
1919D–MICRO–6/08
AT89S52
Figure 16-2. External Clock Drive Configuration
17. Program Memory Lock Bits
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.
Table 16-1.
Status of External Pins During Idle and Power-down Modes
Mode
Program
Memory
ALE
PSEN
PORT0
PORT1
PORT2
PORT3
Idle
Internal
1
1
Data
Data
Data
Data
Idle
External
1
1
Float
Data
Address
Data
Power-down
Internal
0
0
Data
Data
Data
Data
Power-down
External
0
0
Float
Data
Data
Data
XTAL2
XTAL1
GND
NC
EXTERNAL
OSCILLATOR
SIGNAL
Table 17-1.
Lock Bit Protection Modes
Program Lock Bits
LB1
LB2
LB3
Protection Type
1
U
U
U
No program lock features
2P
U
U
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
3
P
P
U
Same as mode 2, but verify is also disabled
4
P
P
P
Same as mode 3, but external execution is also disabled




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