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ST92F124/F150/F250 - INTERRUPTS

5 INTERRUPTS

5.1 INTRODUCTION

The ST9 responds to peripheral and external

events through its interrupt channels. Current pro-

gram execution can be suspended to allow the

ST9 to execute a specific response routine when

such an event occurs, providing that interrupts

have been enabled, and according to a priority

mechanism. If an event generates a valid interrupt

request, the current program status is saved and

control passes to the appropriate Interrupt Service

Routine.

The ST9 CPU can receive requests from the fol-

lowing sources:

– On-chip peripherals

– External pins

– Top-Level Pseudo-non-maskable interrupt

5.1.1 On-Chip Peripheral Interrupt Sources

5.1.1.1 Dedicated Channels

The following on-chip peripherals have dedicated

interrupt channels with interrupt control registers

located in their peripheral register page.

– A/D Converter

– I2C

– JPBLD

– MFT

– SCI-M

5.1.1.2 Standard Channels

Other on-chip peripherals have their interrupts

mapped to the INTxx interrupt channel group.

These channels have control registers located in

Pages 0 and 60. These peripherals are:

– CAN

– E3 TM/FLASH

– EFT Timer

– RCCU

– SCI-A

– SPI

– STIM timer

– WDT Timer

– WUIMU

5.1.1.3 External Interrupts

Up to eight external interrupts, with programmable

input trigger edge, are available and are mapped

to the INTxx interrupt channel group in page 0.

5.1.1.4 Top Level Interrupt (TLI)

In addition, a dedicated interrupt channel, set to

the Top-level priority, can be devoted either to the

external NMI pin (where available) to provide a

Non-Maskable Interrupt, or to the Timer/Watch-

dog. Interrupt service routines are addressed

through a vector table mapped in Memory.

Figure 44. Interrupt Response

5.2 INTERRUPT VECTORING

The ST9 implements an interrupt vectoring struc-

ture which allows the on-chip peripheral to identify

the location of the first instruction of the Interrupt

Service Routine automatically.

When an interrupt request is acknowledged, the

peripheral interrupt module provides, through its

Interrupt Vector Register (IVR), a vector to point

into the vector table of locations containing the

start addresses of the Interrupt Service Routines

(defined by the programmer).

Each peripheral has a specific IVR mapped within

its Register File pages (or in register page 0 or 60

if it is mapped to one of the INTxx channels).

The Interrupt Vector table, containing the address-

es of the Interrupt Service Routines, is located in

the first 256 locations of Memory pointed to by the

ISR register, thus allowing 8-bit vector addressing.

For a description of the ISR register refer to the

chapter describing the MMU.

The user Power on Reset vector is stored in the

first two physical bytes in memory, 000000h and

000001h.

NORMAL

PROGRAM

FLOW

INTERRUPT

SERVICE

ROUTINE

IRET

INSTRUCTION

INTERRUPT

VR001833

CLEAR

PENDING BIT

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