USER'S GUIDE

INTERRUPT PRIORITIES

The Secure Microcontroller provides a three priority interrupt scheme. Multiple priority levels allow higher priority sources to interrupt lower priority ISRs. The Power±fail Warning Interrupt automatically has the highest priority if enabled. The remaining interrupts can be programmed by the user to either high or low priority. The priority scheme woks as follows. The ISR for a low priority source can be interrupted by a high priority source. A low priority ISR can not be interrupted by another low priory source. Neither can a high priority ISR be interrupted by a another high priority source. The PFW source will interrupt any ISR if activated.

In the case of simultaneous interrupt requests, the mi- crocontroller has a natural scheme to arbitrate. First, if high and low priority interrupt requests are received simultaneously, then the high priority source will be serviced. If two or more requests from equal priority sources are received, the following natural priority scheme will be used to arbitrate.

Each interrupt priority is determined by an individual bit as shown below. Setting the appropriate bit to a logic 1 will cause that interrupt to be high priority.

PRIORITY

FLAG

INTERRUPT SOURCE

 

 

 

1

PFW

Power±fail Warning

 

 

 

2

IE0

External Interrupt 0

 

 

 

3

TF0

Timer 0 Interrupt

 

 

 

4

IE1

External Interrupt 1

 

 

 

5

TF1

Timer 1 Interrupt

 

 

 

6

RI+TI

Serial I/O Interrupt

 

 

 

INTERRUPT PRIORITY CONTROL BITS Figure 11±3

Bit Description:

All bits are read/write at any time and are cleared to 0 following any hardware reset.

IP.4:

PS

ªSerial Port Priorityº:

Programs Serial Port interrupts for high priority when set to 1. Low priority is

 

selected when cleared to 0.

IP.3:

PT1

ªTimer 1 Priorityº:

Programs Timer 1 interrupt for high priority when set to 1. Low priority is se-

 

lected when cleared to 0.

IP.2:

PX1

ªExt. Int. 1 Priorityº:

Programs External Interrupt 1 for high priority when set to 1. Low priority is

 

selected when cleared to 0.

IP.1:

PT0

ªTimer 0 Priorityº:

Program Timer 0 interrupt for high priority when set to 1. Low priority is se-

 

lected when cleared to 0.

IP.0:

PX0

ªExt. Int. 0 Priorityº:

Programs External Interrupt 0 for high priority when set to 1. Low priority is

 

selected when cleared to 0.

 

 

 

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Mitsubishi DS5000TK, DS907x SIP manual Interrupt Priorities, Interrupt Priority Control Bits ±3 Bit Description, IP.4