ST62T35B datasheet(25/82 Pages) STMICROELECTRONICS

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ST62T35B/E35B

3.3 INTERRUPTS

The CPU can manage four Maskable Interrupt

sources, in addition to a Non Maskable Interrupt

source (top priority interrupt). Each source is as-

sociated with a specific Interrupt Vector which

contains a Jump instruction to the associated in-

terrupt service routine. These vectors are located

in Program space (see Table 8 ).

When an interrupt source generates an interrupt

request, and interrupt processing is enabled, the

PC register is loaded with the address of the inter-

rupt vector (i.e. of the Jump instruction), which

then causes a Jump to the relevant interrupt serv-

ice routine, thus servicing the interrupt.

Interrupt sources are linked to events either on ex-

ternal pins, or on chip peripherals. Several events

can be ORed on the same interrupt source, and

relevant flags are available to determine which

event triggered the interrupt.

The Non Maskable Interrupt request has the high-

est priority and can interrupt any interrupt routine

at any time; the other four interrupts cannot inter-

rupt each other. If more than one interrupt request

is pending, these are processed by the processor

core according to their priority level: source #1 has

the higher priority while source #4 the lower. The

priority of each interrupt source is fixed.

Table 8. Interrupt Vector Map

3.3.1 Interrupt request

All interrupt sources but the Non Maskable Inter-

rupt source can be disabled by setting accordingly

the GEN bit of the Interrupt Option Register (IOR).

This GEN bit also defines if an interrupt source, in-

cluding the Non Maskable Interrupt source, can

restart the MCU from STOP/WAIT modes.

Interrupt request from the Non Maskable Interrupt

source #0 is latched by a flip flop which is auto-

matically reset by the core at the beginning of the

non-maskable interrupt service routine.

Interrupt request from source #1 can be config-

ured either as edge or level sensitive by setting

accordingly the LES bit of the Interrupt Option

Interrupt request from source #2 are always edge

sensitive. The edge polarity can be configured by

setting accordingly the ESB bit of the Interrupt Op-

tion Register (IOR).

Interrupt request from sources #3 & #4 are level

sensitive.

In edge sensitive mode, a latch is set when a edge

occurs on the interrupt source line and is cleared

when the associated interrupt routine is started.

So, the occurrence of an interrupt can be stored,

until completion of the running interrupt routine be-

fore being processed. If several interrupt requests

occurs before completion of the running interrupt

routine, only the first request is stored.

Storage of interrupt requests is not available in

level sensitive mode. To be taken into account,

the low level must be present on the interrupt pin

when the MCU samples the line after instruction

execution.

At the end of every instruction, the MCU tests the

interrupt lines: if there is an interrupt request the

next instruction is not executed and the appropri-

ate interrupt service routine is executed instead.

Table 9. Interrupt Option Register Description

Interrupt Source

Priority

Vector Address

Interrupt source #0

(FFCh-FFDh)

Interrupt source #1

(FF6h-FF7h)

Interrupt source #2

(FF4h-FF5h)

Interrupt source #3

(FF2h-FF3h)

Interrupt source #4

(FF0h-FF1h)

GEN

SET

Enable all interrupts

CLEARED

Disable all interrupts

ESB

SET

Rising edge mode on inter-

rupt source #2

CLEARED

Falling edge mode on inter-

rupt source #2

LES

SET

Level-sensitive mode on in-

terrupt source #1

CLEARED

Falling edge mode on inter-

rupt source #1

OTHERS

NOT USED

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