AT89C51RC datasheet(21/36 Pages) ATMEL

21 / 36 page

1920C–MICRO–03/05

AT89C51RC

20. Program Memory Lock Bits

The AT89C51RC has three lock bits that can be left unprogrammed (U) or can be programmed

(P) to obtain the additional features listed in Table 20-1.

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.

21. Programming the Flash

The AT89C51RC 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 AT89C51RC code memory array is programmed byte-by-byte.

Programming Algorithm: Before programming the AT89C51RC, the address, data, and con-

trol signals should be set up according to Table 22-1 and Figures 22-1 and 22-2. To program the

AT89C51RC, 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/V

PP to 12V.

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 20-1.

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

AT89C51RC Datasheet(PDF) 21 Page - ATMEL Corporation