AT89C51RC-24AI datasheet(21/37 Pages) ATMEL

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AT89C51RC

1920B–MICRO–11/02

Figure 9. External Clock Drive Configuration

Program Memory

Lock Bits

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.

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.

XTAL2

XTAL1

GND

EXTERNAL

OSCILLATOR

SIGNAL

Table 6. Status of External Pins During Idle and Power-down Modes

Mode

Program Memory

ALE

PSEN

PORT0

PORT1

PORT2

PORT3

Idle

Internal

Data

Idle

External

Float

Data

Address

Data

Power-down

Internal

Data

Power-down

External

Float

Data

Table 7. Lock Bit Protection Modes

Program Lock Bits

LB1

LB2

LB3

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

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