AT89S8252-16AA ATMEL Corporation, AT89S8252-16AA Datasheet - Page 18

• Manufacturer Part Number: AT89S8252-16AA
• Description: 8-Bit Microcontroller with 8K Bytes Flash
• Manufacturer: ATMEL Corporation

Program Memory Lock Bits
The AT89S8252 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
Lock Bit Protection Modes
Notes:
Programming the Flash and EEPROM
Atmel’s AT89S8252 Flash Microcontroller offers 8K bytes
of in-system reprogrammable Flash Code memory and 2K
bytes of EEPROM Data memory.
The AT89S8252 is normally shipped with the on-chip Flash
Code and EEPROM Data memory arrays in the erased
state (i.e. contents = FFH) and ready to be programmed.
This device supports a High-Voltage (12V) Parallel pro-
gramming mode and a Low-Voltage (5V) Serial program-
ming mode. The serial programming mode provides a con-
venient way to download the AT89S8252 inside the user’s
system. The parallel programming mode is compatible with
conventional third party Flash or EPROM programmers.
The Code and Data memory arrays are mapped via sepa-
rate address spaces in the serial programming mode. In
the parallel programming mode, the two arrays occupy one
contiguous address space: 0000H to 1FFFH for the Code
array and 2000H to 27FFH for the Data array.
The Code and Data memory arrays on the AT89S8252 are
programmed byte-by-byte in either programming mode. An
auto-erase cycle is provided with the self-timed program-
ming operation in the serial programming mode. There is
no need to perform the Chip Erase operation to reprogram
any memory location in the serial programming mode
unless any of the lock bits have been programmed.
In the parallel programming mode, there is no auto-erase
cycle. To reprogram any non-blank byte, the user needs to
use the Chip Erase operation first to erase both arrays.
4-122
1
2
3
4
Program Lock Bits
2. P = Programmed
1. U = Unprogrammed
LB1
U
P
P
P
LB2
U
U
P
P
LB3
AT89S8252
U
U
U
P
Protection Type
No internal memory lock feature.
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 (parallel or serial mode) is disabled.
Same as Mode 2, but parallel or serial verify are also disabled.
Same as Mode 3, but external execution is also disabled.
(1)(2)
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.
Once programmed, the lock bits can only be unpro-
grammed with the Chip Erase operations in either the par-
allel or serial modes.
Parallel Programming Algorithm
To program and verify the AT89S8252 in the parallel pro-
gramming mode, the following sequence is recommended:
1. Power-up sequence:
2. Set PSEN pin to “L”
3. Apply the appropriate combination of “H” or “L” logic
4. Apply the desired byte address to pins P1.0 to P1.7
5. Raise EA/V
6. Pulse ALE/PROG once to program a byte in the Code
7. To verify the byte just programmed, bring pin P2.7 to
Apply power between V
Set RST pin to “H”.
Apply a 3 MHz to 24 MHz clock to XTAL1 pin and wait
for at least 10 milliseconds.
ALE pin to “H”
EA pin to “H” and all other pins to “H”.
levels to pins P2.6, P2.7, P3.6, P3.7 to select one of the
programming operations shown in the Flash Program-
ming Modes table.
and P2.0 to P2.5.
Apply data to pins P0.0 to P0.7 for Write Code opera-
tion.
erase or verification.
memory array, the Data memory array or the lock bits.
The byte-write cycle is self-timed and typically takes
1.5 ms.
“L” and read the programmed data at pins P0.0 to P0.7.
PP
to 12V to enable Flash programming,
CC
and GND pins.