AT91SAM7:

 

1. Protection:

AT91SAM7 series microcontrollers use a single Security Bit to protect the embedded Flash memory. This bit is part of the General-Purpose Non-Volatile Memory (GPNVM) and controls access to the entire program memory.

 

1.1 The GPNVM[0] Security Bit:

When this bit is set, it completely blocks any external access (read, write, erase) to the Flash memory through the debug port (JTAG/ICE) and the SAM-BA bootloader. However, the processor core can still execute code from the protected memory.

Security Bit States:

GPNVM[0] State Protection Description 0 (unprogrammed) Protection is disabled. Access to Flash via JTAG and SAM-BA is allowed. 1 (programmed) Protection is enabled. All access to Flash via JTAG and SAM-BA is blocked.

 

1.2 Disabling Protection:

Disabling the security bit is possible only through a hardware Chip Erase procedure. It cannot be done via software or the debug interface.

Chip Erase Procedure:

1. Apply a high logic level to the dedicated `ERASE` pin (often shared with a JTAG pin, such as TDI).
2. While holding the `ERASE` pin high, perform a hardware reset of the microcontroller (via the NRST pin).

WARNING: This operation completely and irreversibly erases the entire Flash memory of the microcontroller. After this procedure, the GPNVM[0] security bit is cleared to '0'.

 

1.3 Boot Selection (GPNVM[1]):

Another important bit, GPNVM[1], determines where the microcontroller will boot from after a reset.

GPNVM[1] State Boot Source 0 (unprogrammed) Boot from the embedded Flash memory (standard mode). 1 (programmed) Boot from the embedded ROM, which contains the SAM-BA bootloader.

Note: Even if booting from SAM-BA is forced, access to the Flash memory will still be blocked if the GPNVM[0] security bit is set.

 

2. Unique Identifier (Chip ID):

AT91SAM7 series microcontrollers contain a 32-bit Chip ID register, which is unique for each die. It can be read at any time (even when the security bit is set) and is ideal for:

 

Microchip Technology (SAM MCUs)

 

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