AT89C52-24PC datasheet(13/24 Pages) ATMEL

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AT89C52

Program Memory Lock Bits

The AT89C52 has three lock bits that can be left unpro-

grammed (U) or can be programmed (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 during reset. If the device is pow-

ered 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.

Programming the Flash

The AT89C52 is normally shipped with the on-chip Flash

memory array in the erased state (that is, contents = FFH)

and ready to be programmed. The programming interface

accepts either a high-voltage (12-volt) or a low-voltage

CC) program enable signal. The Low-voltage program-

ming mode provides a convenient way to program the

AT89C52 inside the user’s system, while the high-voltage

programming mode is compatible with conventional third-

party Flash or EPROM programmers.

The AT89C52 is shipped with either the high-voltage or

low-voltage programming mode enabled. The respective

top-side marking and device signature codes are listed in

the following table.

The AT89C52 code memory array is programmed byte-by-

byte in either programming mode. To program any non-

blank byte in the on-chip Flash Memory, the entire memory

must be erased using the Chip Erase Mode.

Programming Algorithm Before programming the

AT89C52, the address, data and control signals should be

set up according to the Flash programming mode table and

Figure 9 and Figure 10. To program the AT89C52, take the

following steps.

Input the desired memory location on the address

lines.

Input the appropriate data byte on the data lines.

Activate the correct combination of control signals.

Raise EA/VPP to 12V for the high-voltage program-

ming mode.

Pulse ALE/PROG once to program a byte in the

Flash array or the lock bits. The byte-write cycle is

self-timed and typically takes no more than 1.5 ms.

Repeat steps 1 through 5, changing the address

and data for the entire array or until the end of the

object file is reached.

Data Polling The AT89C52 features Data Polling to indi-

cate the end of a write cycle. During a write cycle, an

attempted read of the last byte written will result in the com-

plement of the written data on PO.7. Once the write cycle

has been completed, true data is valid on all outputs, and

the next cycle may begin. Data Polling may begin any time

after a write cycle has been initiated.

Ready/Busy The progress of byte programming can also

be monitored by the RDY/BSY output signal. P3.4 is pulled

low after ALE goes high during programming to indicate

BUSY. P3.4 is pulled high again when programming is

done to indicate READY.

Program Verify If lock bits LB1 and LB2 have not been

programmed, the programmed code data can be read back

via the address and data lines for verification. The lock bits

cannot be verified directly. Verification of the lock bits is

achieved by observing that their features are enabled.

Chip Erase The entire Flash array is erased electrically by

using the proper combination of control signals and by

holding ALE/PROG low for 10 ms. The code array is written

with all 1s. The chip erase operation must be executed

before the code memory can be reprogrammed.

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.

PP = 12V

PP = 5V

Top-side Mark

AT89C52

xxxx

yyww

AT89C52

xxxx - 5

yyww

Signature

(030H) = 1EH

(031H) = 52H

(032H) = FFH

(030H) = 1EH

(031H) = 52H

(032H) = 05H

PP = 12V

PP = 5V

AT89C52-24PC Datasheet(PDF) 13 Page - ATMEL Corporation

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