AT89C51RC-33AC ATMEL Corporation, AT89C51RC-33AC Datasheet - Page 21

• Manufacturer Part Number: AT89C51RC-33AC
• Description: 8-bit Microcontroller with 32K Bytes Flash
• Manufacturer: ATMEL Corporation

Table 6. Status of External Pins During Idle and Power-down Modes
Program Memory
Lock Bits
1920B–MICRO–11/02
Mode
Idle
Idle
Power-down
Power-down
Program Memory
Internal
External
Internal
External
Figure 9. External Clock Drive Configuration
The AT89C51RC has three lock bits that can be left unprogrammed (U) or can be pro-
grammed (P) to obtain the additional features listed in the following table.
Table 7. Lock Bit Protection Modes
When lock bit 1 is programmed, the logic level at the EA pin is sampled and latched dur-
ing 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.
1
2
3
4
Program Lock Bits
LB1
U
P
P
P
ALE
1
1
0
0
LB2
U
U
P
P
OSCILLATOR
EXTERNAL
SIGNAL
PSEN
NC
1
LB3
1
0
0
U
U
U
P
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
PORT0
Float
Data
Data
Float
XTAL2
XTAL1
GND
PORT1
Data
Data
Data
Data
AT89C51RC
Address
PORT2
Data
Data
Data
PORT3
Data
Data
Data
Data
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