AT89C51-12 ATMEL [ATMEL Corporation], AT89C51-12 Datasheet - Page 5

• Manufacturer Part Number: AT89C51-12
• Description: 8-Bit Microcontroller with 4K Bytes Flash
• Manufacturer: ATMEL [ATMEL Corporation]

Power Down Mode
In the power down mode the oscillator is stopped, and the
instruction that invokes power down is the last instruction
executed. The on-chip RAM and Special Function Regis-
ters retain their values until the power down mode is termi-
nated. The only exit from power down is a hardware reset.
Reset redefines the SFRs but does not change the on-chip
RAM. The reset should not be activated before V
restored to its normal operating level and must be held
active long enough to allow the oscillator to restart and sta-
bilize.
Lock Bit Protection Modes
Programming the Flash
The AT89C51 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
(V
ming mode provides a convenient way to program the
AT89C51 inside the user’s system, while the high-voltage
programming mode is compatible with conventional third
party Flash or EPROM programmers.
The AT89C51 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 AT89C51 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.
Top-Side Mark
Signature
CC
1
2
3
4
) program enable signal. The low voltage program-
Program Lock Bits
LB1
U
P
P
P
LB2
U
U
P
P
V
AT89C51
xxxx
yyww
(030H)=1EH
(031H)=51H
(032H)=FFH
PP
LB3
= 12V
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 is disabled.
Same as mode 2, also verify is disabled.
Same as mode 3, also external execution is disabled.
V
AT89C51
xxxx-5
yyww
(030H)=1EH
(031H)=51H
(032H)=05H
PP
= 5V
CC
is
Program Memory Lock Bits
On the chip are three lock bits which can be left unpro-
grammed (U) or can be programmed (P) to obtain the addi-
tional features listed in the table below:
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. It is nec-
essary that the latched value of EA be in agreement with
the current logic level at that pin in order for the device to
function properly.
Programming Algorithm: Before programming the
AT89C51, the address, data and control signals should be
set up according to the Flash programming mode table and
Figures 3 and 4. To program the AT89C51, take the follow-
ing steps.
1. Input the desired memory location on the address
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
Data Polling: The AT89C51 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 datum on PO.7. Once the write cycle
has been completed, true data are 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.
lines.
mode.
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.
PP
to 12V for the high-voltage programming
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