COP8-REF-AM datasheet(57/83 Pages) NSC

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18.0 Interrupts

18.1 INTRODUCTION

The device supports fourteen vectored interrupts. Interrupt

sources include Timer 1, Timer 2, Timer 3, Timer T0, Port L

Wake-up, Software Trap, MICROWIRE/PLUS, USART and

External Input.

All interrupts force a branch to location 00FF Hex in program

memory. The VIS instruction may be used to vector to the

appropriate service routine from location 00FF Hex.

The Software trap has the highest priority while the default

VIS has the lowest priority.

Each of the 13 maskable inputs has a fixed arbitration rank-

ing and vector.

Figure 31 shows the Interrupt block diagram.

18.2 MASKABLE INTERRUPTS

All interrupts other than the Software Trap are maskable.

Each maskable interrupt has an associated enable bit and

pending flag bit. The pending bit is set to 1 when the interrupt

condition occurs. The state of the interrupt enable bit, com-

bined with the GIE bit determines whether an active pending

flag actually triggers an interrupt. All of the maskable inter-

rupt pending and enable bits are contained in mapped con-

trol registers, and thus can be controlled by the software.

A maskable interrupt condition triggers an interrupt under the

following conditions:

The enable bit associated with that interrupt is set.

The GIE bit is set.

The device is not processing a non-maskable interrupt.

(If a non-maskable interrupt is being serviced, a

maskable interrupt must wait until that service routine is

completed.)

An interrupt is triggered only when all of these conditions are

met at the beginning of an instruction. If different maskable

interrupts meet these conditions simultaneously, the highest-

priority interrupt will be serviced first, and the other pending

interrupts must wait.

Upon Reset, all pending bits, individual enable bits, and the

GIE bit are reset to zero. Thus, a maskable interrupt condi-

tion cannot trigger an interrupt until the program enables it by

setting both the GIE bit and the individual enable bit. When

enabling an interrupt, the user should consider whether or

not a previously activated (set) pending bit should be ac-

knowledged. If, at the time an interrupt is enabled, any

previous occurrences of the interrupt should be ignored, the

associated pending bit must be reset to zero prior to en-

abling the interrupt. Otherwise, the interrupt may be simply

20006332

FIGURE 31. Interrupt Block Diagram

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