Maxim-integrated MAXQ622 Manual do Utilizador descarregar pdf (Página 26)

MAXQ612/MAXQ622 User’s Guide

2-22 Maxim Integrated

2.6.7 Loader Access Control

As stated previously, the MAXQ612/MAXQ622 have three memory regions: system, user loader, and application. The

loader maintains a context register to determine which of the regions is to be the target of the loader commands. Family

0 and Family F commands have no context. They are global in scope. For details on the nonparty-specific loader com-

mands, refer to Application Note 4012: Implementing a JTAG Bootloader Master for the MAXQ2000 Microcontroller.

There are two Family F loader commands specific to the MAXQ612/MAXQ622:

Command 0xF0: GetContext

Input : None

Output : Context Byte – 00x00, SystemContext; 0x01, LoaderContext; 0x2, ApplicationContext

Command 0xF1” SetContext

Input : Context Byte – 0x00, SystemContext; 0x01, LoaderContext; 0x02, ApplicationContext

Output : Sets Error Code (retrieved using Getstatus bootloader command)

The bootloader sets a default context based on the lowest privileged region that exists. The default context is selected

according to the following rules:

If all three regions exist:

The user application context (UAPP_CONTEXT).

If only system and user application regions exist:

The user application context.

If only system and user loader regions exist:

The user loader context (ULDR_CONTEXT).

If only the system region exists:

The system context (SYSTEM)CONTEXT). Only the default context will have its password tested and

corresponding PWL bit cleared. The context can be changed through the Family F commands shown above, but the

password for the new region is not tested after a context change and, therefore, a password match loader command

must be sent to clear the password lock bit of the associated region even if the password for that region is clear.

If the system password has not been set, memory protection is disabled by the ROM. If word address 000Eh in the

system code region is programmed (any value other than 0xFFFF), the debug lockout condition is set by setting

SC.DBGLCK to 1 (all debug functions are disabled).

The “current context” is used by the loader to determine how to apply master erase and password-protected loader

commands. The master erase command erases pages starting at the base address of the current context and all

pages with addresses greater than the base address. Password-protected commands check the password lock bit of

the current region. The unlock password command uses the password from the current region (indicated by the current

context) to determine the state of the current region password lock.

The loader provides several commands that require a password and a master erase command that does not.

All password-protected commands check the following:

• System password match: Access to full memory

• Loader password match: Access to user memory

• Application password match: Access to user application memory

• No match: No access

Three PWL bits allow the loader to find out whether a password match was successful. The PWL bits for system and

user loader can only be written by utility ROM code (see Section 15.2 Password-Protected Access).

Master erase does not require a password and defaults to erasing the user application only. Two Family F commands

are added that allow master erase of user loader and system code:

• Master erase system: Complete system erase.

• Master erase user loader: Erases user loader and user application.

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