AT90S/LS4434 and AT90S/LS8535
85
Memory Programming
Program and Data Memory Lock Bits
The AT90S4434/8535 MCU provides two Lock bits that can be left unprogrammed (“1”) or can be programmed (“0”) to
obtain the additional features listed in Table 36. The Lock bits can only be erased with the Chip Erase command.
Note:
1. In Parallel Mode, further programming of the Fuse bits is also disabled. Program the Fuse bits before programming the Lock
bits.
Fuse Bits
The AT90S4434/8535 has two Fuse bits, SPIEN and FSTRT.
• When the SPIEN Fuse is programmed (“0”), Serial Program and Data Downloading is enabled. Default value is
programmed (“0”). The SPIEN Fuse is not accessible in Serial Programming Mode.
• When the FSTRT Fuse is programmed (“0”), the short start-up time is selected. Default value is unprogrammed (“1”).
The status of the Fuse bits is not affected by Chip Erase.
Signature Bytes
All Atmel microcontrollers have a three-byte signature code that identifies the device. This code can be read in both Serial
and Parallel modes. The three bytes reside in a separate address space.
For the AT90S4434
, they are:
1.
$000: $1E (indicates manufactured by Atmel)
2.
$001: $92 (indicates 4K bytes Flash memory)
3.
$002: $02 (indicates AT90S4434 device when signature byte $001 is $92)
For the AT90S8535
, they are:
1.
$000: $1E (indicates manufactured by Atmel)
2.
$001: $93 (indicates 8K bytes Flash memory)
3.
$002: $03 (indicates AT90S8535 device when signature byte $001 is $93)
Note:
1. When both Lock bits are programmed (lock mode 3), the signature bytes cannot be read in Serial Mode. Reading the
signature bytes will return: $00, $01 and $02.
Programming the Flash and EEPROM
Atmel’s AT90S4434/8535 offers 4K/8K bytes of in-system reprogrammable Flash program memory and 256/512 bytes of
EEPROM data memory.
The AT90S4434/8535 is shipped with the on-chip Flash program and EEPROM data memory arrays in the erased state
(i.e., contents = $FF) and ready to be programmed. This device supports a high-voltage (12V) Parallel Programming Mode
and a low-voltage Serial Programming Mode. The +12V is used for programming enable only and no current of significance
is drawn by this pin. The Serial Programming Mode provides a convenient way to download program and data into the
AT90S4434/8535 inside the user’s system.
Table 36.
Lock Bit Protection Modes
Memory Lock Bits
Protection Type
Mode
LB1
LB2
1
1
1
No memory lock features enabled.
2
0
1
Further programming of the Flash and EEPROM is disabled.
3
0
0
Same as mode 2 and verify is also disabled.