ST92F120JR9T datasheet(287/320 Pages) STMICROELECTRONICS

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EIGHT-CHANNEL ANALOG TO DIGITAL CONVERTER (A/D)

ANALOG TO DIGITAL CONVERTER (Cont’d)

Figure 123. Application Example: Analog Watchdog used in Motorspeed Control

10.9.3 Interrupts

The A/D provides two interrupt sources:

– End of Conversion

– Analog Watchdog Request

The A/D Interrupt Vector Register (AD_IVR) pro-

vides hardware generated flags which indicate the

interrupt source, thus allowing automatic selection

of the correct interrupt service routine.

The A/D Interrupt vector should be programmed

by the User to point to the first memory location in

the Interrupt Vector table containing the base ad-

dress of the four byte area of the interrupt vector

table in which the address of the A/D interrupt

service routines are stored.

The Analog Watchdog Interrupt Pending bit (AWD,

AD_ICR.6), is automatically set by hardware

whenever any of the two guarded analog inputs go

out of range. The Compare Result Register (CRR)

tracks the analog inputs which exceed their pro-

grammed thresholds.

When two requests occur simultaneously, the An-

alog Watchdog Request has priority over the End

of Conversion request, which is held pending.

The Analog Watchdog Request requires the user

to poll the Compare Result Register (CRR) to de-

termine which of the four thresholds has been ex-

ceeded. The threshold status bits are set to flag an

out of range condition, and are automatically reset

by hardware after a software reset of the Analog

Watchdog Request flag in the AD_ICR Register.

The interrupt pending flags, ECV and AWD,

should be reset by the user within the interrupt

service routine. Setting either of these two bits by

software will cause an interrupt request to be gen-

erated.

10.9.3.1 Register Mapping

It is possible to have two independent A/D convert-

ers in the same device. In this case they are

named A/D 0 and A/D 1. If the device has one A/D

converter it uses the register addresses of A/D 0.

The register pages are the following:

Analog

Watch-

dog Re-

quest

Lower

Word

Address

End of

Conv.

Request

Upper

Word

Address

A/Dn

A/D 0

A/D 1

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