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Memory
Programming
Program and Data
Memory Lock Bits
Fuse Bits
Signature Bytes
Programming the Flash
and EEPROM
0838H–AVR–03/02
The AT90S1200 MCU provides two Lock bits that can be left unprogrammed ("1") or can
be programmed ("0") to obtain the additional features listed in Table 12. The Lock bits
can only be erased with the Chip Erase command.
Table 12. Lock Bit Protection Modes
Memory Lock Bits
Mode
LB1
LB2
Protection Type
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.
Note:
1. In Parallel mode, further programming of the Fuse bits are also disabled. Program
the Fuse bits before programming the Lock bits.
The AT90S1200 has two Fuse bits: SPIEN and RCEN.
•
When the SPIEN Fuse bit is programmed ("0"), Serial Program Downloading is
enabled. Default value is programmed ("0").
•
When the RCEN Fuse bit is programmed ("0"), MCU clocking from the Internal RC
Oscillator is selected. Default value is erased ("1"). Parts with this bit pre-
programmed ("0") can be delivered on demand.
•
The Fuse bits are not accessible in Serial Programming mode. The status of the
Fuse bits is not affected by Chip Erase.
All Atmel microcontrollers have a 3-byte signature code that identifies the device. This
code can be read in both Serial and Parallel modes. The three bytes reside in a sepa-
rate address space.
For the AT90S1200 they are:
1. $00: $1E (indicates manufactured by Atmel)
2. $01: $90 (indicates 1 Kb Flash memory)
3. $02: $01 (indicates AT90S1200 device when $01 is $90)
Note:
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.
Atmel's AT90S1200 offers 1K byte of in-System Reprogrammable Flash program mem-
ory and 64 bytes of EEPROM data memory.
The AT90S1200 is normally shipped with the On-chip Flash program memory 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 AT90S1200
inside the user's system.
The program and data memory arrays on the AT90S1200 are programmed byte-by-byte
in either programming mode. For the EEPROM, an auto-erase cycle is provided within
AT90S1200
(1)
37
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