at89lv55 ATMEL Corporation, at89lv55 Datasheet - Page 17

• Manufacturer Part Number: at89lv55
• Description: At89lv55 8-bit Microcontroller With 20k Bytes Flash
• Manufacturer: ATMEL Corporation

16. Program Memory Lock Bits
17. Programming the Flash
0811D–MICRO–3/06
The AT89LV55 has three lock bits that can be left unprogrammed (U) or can be programmed (P)
to obtain the additional features listed in
Table 16-1.
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 AT89LV55 code memory array is programmed byte-by-byte. To program any non-blank
byte in the on-chip Flash Memory, the entire memory must be erased using the Chip
Erase Mode.
The AT89LV55 is normally shipped with the on-chip Flash memory array in the erased state
(that is, contents = FFH) and ready to be programmed.
Programming Algorithm: Before programming the AT89LV55, the address, data and control
signals should be set up according to
Figure
Data Polling: The AT89LV55 features Data Polling to indicate the end of a write cycle. During a
write cycle, an attempted read of the last byte written will result in the complement of the written
data on PO.7. Once the write cycle has been completed, true data is 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/BUSY out-
put 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.
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
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.
18-1. To program the AT89LV55, take the following steps:
Program Lock Bits
LB1
U
P
P
P
Lock Bit Protection Modes
PP
LB2
to 12V
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.
Table 18-1, “Flash Programming Modes,” on page 19
Table
16-1:
AT89LV55
and
17