MSM80C154S/83C154S/85C154HVS

4.7.3.2 Interrupt routine flow when priority circuit is stopped

When bit 7 (PCT) of the priority register (IP 0B8H) is set to “1”, all interrupt control is transferred to the interrupt enable register (IE 0A8H). When this mode is set, the interrupt disable instruction (CLR EA) must always be placed at the beginning of the interrupt routine to prevent any other interrupt from being generated. If another interrupt routine have to be generated during the processing of an interrupt routine, set the desired interrupt enable bit in the interrupt enable register (IE 0A8H) to commence the new interrupt routine. Multi-level interrupt processing can thus be achieved by control of the interrupt enable register. The flow of this interrupt routine is shown in Figure 4-46.

Main routine

M

CLREA

CLREA

CLREA

CLREA

EA

EA

EA

EA

Generation

Generation

Generation

Generation

of interrput

of interrput

of interrput

of interrput

EA

RETI

M

Main routine

RETI

RETI

Interrput routine

RETI

Figure 4-46 lnterrupt routine flow chart when priority circuit is stopped

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