ST90R158 datasheet(168/190 Pages) STMICROELECTRONICS

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ST90158 - EIGHT-CHANNEL ANALOG TO DIGITAL CONVERTER (A/D)

ANALOG TO DIGITAL CONVERTER (Cont’d)

Analog channels 6 and 7 monitor an acceptable

voltage level window for the converted analog in-

puts. The external voltages applied to inputs 6 and

7 are considered normal while they remain below

their respective Upper thresholds, and above or at

their respective Lower thresholds.

When the external signal voltage level is greater

than, or equal to, the upper programmed voltage

limit, or when it is less than the lower programmed

voltage limit, a maskable interrupt request is gen-

erated and the Compare Results Register is up-

dated in order to flag the threshold (Upper or Low-

er) and channel (6 or 7) responsible for the inter-

rupt. The four threshold voltages are user pro-

grammable in dedicated registers (08h to 0Bh) of

the A/D register page. Only the 4 MSBs of the

Compare Results Register are used as flags (the 4

LSBs always return “1” if read), each of the four

MSBs being associated with a threshold condition.

Following a hardware reset, these flags are reset.

During normal A/D operation, the CRR bits are set,

in order 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.

9.6.2.4 Power Down Mode

Before enabling an A/D conversion, the POW bit of

the Control Logic Register must be set; this must

be done at least 60

µs before the first conversion

start, in order to correctly bias the analog section

of the converter circuitry.

When the A/D is not required, the POW bit may be

reset in order to reduce the total power consump-

tion. This is the reset configuration, and this state

is also selected automatically when the ST9 is

placed in Halt Mode (following the execution of the

halt

instruction).

Figure 87. A/D Trigger Source

Analog Voltage

Upper threshold

Lower threshold

Normal Area

(Window Guarded)

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