AT89C55WD Atmel Corporation, AT89C55WD Datasheet - Page 20

• Manufacturer Part Number: AT89C55WD
• Manufacturer: Atmel Corporation

Specifications of AT89C55WD

• Flash (kbytes): 20 Kbytes
• Max. Operating Frequency: 24 MHz
• Cpu: 8051-12C
• Max I/o Pins: 32
• Uart: 1
• Sram (kbytes): 0.25
• Operating Voltage (vcc): 4.0 to 6.0
• Timers: 3
• Watchdog: Yes

19. Program Memory Lock Bits
20. Programming the Flash
20
AT89C55WD
The AT89C55WD has three lock bits that can be left unprogrammed (U) or can be programmed
(P) to obtain the additional features listed in the following table.
Table 19-1.
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.
The AT89C55WD 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 AT89C55WD code memory array is programmed byte-by-byte.
Programming Algorithm: Before programming the AT89C55WD, the address, data, and con-
trol signals should be set up according to the Flash programming mode table and Figures 21-1
and 21-2. To program the AT89C55WD, 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-
1
2
3
4
Program Lock Bits
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.
LB1
U
P
P
P
Lock Bit Protection Modes
LB2
PP
U
U
P
P
to 12V.
LB3
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.
1921D–MICRO–6/08