COP8CDR9 datasheet(79/112 Pages) TI1

79 / 112 page

COP8CBR9, COP8CCR9, COP8CDR9

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SNOS535I – OCTOBER 2000 – REVISED MARCH 2013

The Software Trap indicates an unusual or unknown error condition. Generally, returning to normal

execution at the point where the Software Trap occurred cannot be done reliably. Therefore, the Software

Trap service routine should re-initialize the stack pointer and perform a recovery procedure that re-starts

the software at some known point, similar to a device Reset, but not necessarily performing all the same

functions as a device Reset. The routine must also execute the RPND instruction to reset the STPND flag.

Otherwise, all other interrupts will be locked out. To the extent possible, the interrupt routine should record

or indicate the context of the device so that the cause of the Software Trap can be determined.

If the user wishes to return to normal execution from the point at which the Software Trap was triggered,

the user must first execute RPND, followed by RETSK rather than RETI or RET. This is because the

return address stored on the stack is the address of the INTR instruction that triggered the interrupt. The

program must skip that instruction in order to proceed with the next one. Otherwise, an infinite loop of

Software Traps and returns will occur.

Programming a return to normal execution requires careful consideration. If the Software Trap routine is

interrupted by another Software Trap, the RPND instruction in the service routine for the second Software

Trap will reset the STPND flag; upon return to the first Software Trap routine, the STPND flag will have the

wrong state. This will allow maskable interrupts to be acknowledged during the servicing of the first

Software Trap. To avoid problems such as this, the user program should contain the Software Trap

routine to perform a recovery procedure rather than a return to normal execution.

Under normal conditions, the STPND flag is reset by a RPND instruction in the Software Trap service

routine. If a programming error or hardware condition (brownout, power supply glitch, etc.) sets the

STPND flag without providing a way for it to be cleared, all other interrupts will be locked out. To alleviate

this condition, the user can use extra RPND instructions in the main program and in the Watchdog service

routine (if present). There is no harm in executing extra RPND instructions in these parts of the program.

Figure 5-25. VIS Flow Chart

Functional Description

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Product Folder Links: COP8CBR9 COP8CCR9 COP8CDR9

COP8CDR9 Datasheet(PDF) 79 Page - Texas Instruments