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2601B–MICRO–03/05

AT89LS52

17. Program Memory Lock Bits

The AT89LS52 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.

18. Programming the Flash – Parallel Mode

The AT89LS52 is shipped with the on-chip Flash memory array ready to be programmed. The

programming interface needs a high-voltage (12-volt) program enable signal and is compatible

with conventional third-party Flash or EPROM programmers.

The AT89LS52 code memory array is programmed byte-by-byte.

Programming Algorithm: Before programming the AT89LS52, the address, data, and control

signals should be set up according to the Flash programming mode table (Table 20-1) and Fig-

ure 20-1 and Figure 20-2. To program the AT89LS52, take the following steps:

1.

Input the desired memory location on the address lines.

2.

Input the appropriate data byte on the data lines.

3.

Activate the correct combination of control signals.

4.

Raise EA/V

5.

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 50 µs. Repeat steps 1

through 5, changing the address and data for the entire array or until the end of the

object file is reached.

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

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