Maxim Integrated Secure Microcontroller - Manual (Page 89)

Secure Microcontroller User’s Guide
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routine. It can lie any where in the 64kB of program memory addressed by the device. A common choice
is location 0030h. Thus at location 0000h, the user would use the instruction SJMP 30h. This instruction
requires two bytes, so it easily fits in the available space. At the location of the reset routine, the user
places instructions that initialize the microprocessor and any external hardware specific to the application.
This note describes the operations that are typically done and shows some example code. The following
functions are typically initialized in a user’s reset routine:
MEMORY INTERRUPTS TIMERS/SERIAL PROTECTION
Partition Power-fail Timer setup Watchdog Timer
Current Memory Map External Timer for baud-rates POR
Data Pointer Serial Port Serial Port
Timer
10.2 Memory Map
The most critical and most overlooked initialization is that of the memory map. Several of these functions
are nonvolatile and are not cleared during a reset. Those that are cleared could leave the microprocessor
in an undesirable state. Therefore, the user should either verify the correctness of the memory map or
simply set it properly following each reset. An example of how the memory map could be incorrect on
reset is as follows.
The user typically sets the Partition, Range, etc., during Bootstrap Loading. In the course of operating
however, the user may temporarily move the Partition to alter a lookup table. If while the Partition is
moved, a reset should occur, the Partition will remain in the temporary position unless corrected.
In developing the reset routine, the user should carefully note the reset state of each critical bit. For
example, when using the ECE2 on a DS5000FP, note that it is not altered on reset. On a DS5001FP, the
PES bit is cleared on a reset. Thus a DS5000T that is accessing the Real-time Clock when a reset occurs
will still be pointing the CE2 space after reset. The DS2251T user that is accessing the RTC when a reset
occurs will start in the normal memory configuration.
A code example that initializes the memory map is as follows. It assumes that the DS5000FP user
requires a Partition of 5800h. A DS5001FP using the same code would use a Partition of B000h.
MCON EQU 0C6h
Org 00h
SJMP
Start
Org
30h
Start :
MOV
TA, #0Aah ;Timed
MOV TA, #55h ; Access
ORL MCON, #02h ;Set PAA - DS5000 ONLY
MOV MCON, #0B8h ;Set Partition to 5800 on DS5000, B000h on DS5001
MOV TA, #0Aah ;Timed - DS5000 ONLY
MOV TA, #55h ; Access - DS5000 ONLY
ANL MCON, #0FDh ;Clear PAA - DS5000 ONLY
Another common memory requirement is the initialization of the Data Pointer. When using NV RAM to
store data, this pointer must be moved to the Partition address (in a partitionable configuration). Thus if