at89c55-16qa ATMEL Corporation, at89c55-16qa Datasheet - Page 13

• Manufacturer Part Number: at89c55-16qa
• Description: 8-bit Microcontroller With Bytes Flash
• Manufacturer: 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 AT89C55 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
mode provides a convenient way to program the AT89C55
inside the user’s system, while the high-voltage program-
ming mode is compatible with conventional third party
Flash or EPROM programmers.
The AT89C55 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
following table.
Top-Side Mark
Signature
CC
1
2
3
4
) program enable signal. The low voltage programming
Program Lock Bits
LB1
U
P
P
P
LB2
U
U
P
P
LB3
V
AT89C55
xxxx
yyww
(030H) = 1EH
(031H) = 55H
(032H) = FFH
U
U
U
P
PP
= 12V
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.
V
AT89C55
xxxx-5
yyww
(030H) = 1EH
(031H) = 55H
(032H) = 05H
PP
= 5V
CC
is
Program Memory Lock Bits
The AT89C55 has three lock bits that can be left unpro-
grammed (U) or can be programmed (P) to obtain the addi-
tional 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.
The AT89C55 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
AT89C55, the address, data and control signals should be
set up according to the Flash programming mode table and
Figures 9 and 10. To program the AT89C55, take the fol-
lowing 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
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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