at89c55-12qi ATMEL Corporation, at89c55-12qi Datasheet - Page 13

• Manufacturer Part Number: at89c55-12qi
• 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
is restored to its normal operating level and must be held
active long enough to allow the oscillator to restart and
stabilize.
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 ad-
ditional features listed in the following table.
Lock Bit Protection Modes
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 ran-
dom 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.
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
ming mode provides a convenient way to program the
AT89C55 inside the user’s system, while the high-voltage
programming mode is compatible with conventional third
party Flash or EPROM programmers.
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
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.
CC
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
the following table.
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
following 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/VPP to 12V for the high-voltage program-
5. Pulse ALE/PROG once to program a byte in the Flash
Top-Side Mark
Signature
lines.
ming mode.
array or the lock bits. The byte-write cycle is self-
timed and typically takes no more than 1.5 ms. Re-
peat steps 1 through 5, changing the address and
data for the entire array or until the end of the object
file is reached.
AT89C55
xxxx
yyww
(030H) = 1EH
(031H) = 55H
(032H) = FFH
AT89C55
V
PP
= 12V
AT89C55
xxxx-5
yyww
(030H) = 1EH
(031H) = 55H
(032H) = 05H
V
PP
(continued)
= 5V
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