Mitsubishi DS907x SIP, DS5000TK manual Application Reset Routine Example, Memory Map

USER'S GUIDE

APPLICATION: RESET ROUTINE EXAMPLE

Like the 8051, Dallas Semiconductor Microcontrollers will begin execution at address 0000h. This is the Reset Vector, followed by other vector locations used for inter- rupts. These are discussed in the section covering inter- rupt operation. Since there are only three memory loca- tions dedicated to the Reset Vector, the user will typically insert a jump statement to a more convenient memory address. This will be the reset routine. It can lie any where in the 64K bytes 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 loca- tion 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

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.

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