Motorola DSP56000, 24-Bit Digital Signal Processor manual Reset Processing State

RESET PROCESSING STATE

mented to one (see Figure 7-13). During the execution of n2 in Figure 7-13,no interrupts will be serviced. When LC finally decrements to one, the fetches are reinitiated, and pending interrupts can be serviced.

Sequential REP packages will cause pending interrupts to be rejected until the sequence of REP packages ends. REP packages are not interruptible because the instruction being repeated is not refetched. While that instruction is repeating, no instructions are fetched or decoded, and an interrupt can not be inserted. For example, in Figure 7-14,if n1, n3, and n5 are all REP instructions, no interrupts will be serviced until the last REP instruction (n5 and its repeated instruction, n6) completes execution.

7.4RESET PROCESSING STATE

The processor enters the reset processing state when a hardware reset occurs and the external RESET pin is asserted. The reset state:

1.resets internal peripheral devices;

2.sets the modifier registers to $FFFF;

3.clears the interrupt priority register;

4.sets the BCR to $FFFF, thereby inserting 15 wait states in all external memory accesses;

5.clears the stack pointer;

6.clears the scaling mode, trace mode, loop flag, double precision multiply mode, and condition code bits of the SR, and sets the interrupt mask bits of the SR;

7.clears the data ROM enable bit, the stop delay bit, and the internal Y memory disable bit, and

8.the DSP remains in the reset state until the RESET pin is deasserted.

When the processor deasserts the reset state:

9.it loads the chip operating mode bits of the OMR from the external mode select pins (MODA, MODB, MODC), and

10.begins program execution at program memory address defined by the state of bits MODA, MODB, and MODC in the OMR. The first instruction must be fetched and then decoded before executing. Therefore, the first instruction execution is two instruction cycles after the first instruction fetch.

MOTOROLA PROCESSING STATES 7 - 33