ADC9708 datasheet(6/8 Pages) NSC

6 / 8 page

Typical Applications (Continued)

3 The auto-zeroauto-full-scale (See

Figures 5 – 8 ) should

use double precision rounded (as opposed to truncated)

arithmatic Several points are worth noting

a The subtractions are single op code instructions

b The full scale correction uses a multiply by 256 and

can be accomplished by a shift left 8 bits (usually one

instruction) or placing (N b NZ) in the MSB register

and setting the LSB register to zero for the double

precision divide

c The divisor (NFS b NZ) of the MSB register will al-

ways be zero

These schemes have the following advantages

a No access to the data bus or address bus is required

by the AD system

b 5 IO bits completely support the AD system

c Since auto full scaleauto zero are implemented in

software and long term drift (aging) effects are elimi-

nated

d Software overhead is minimal (typically 30 bytes)

e Where ratiometric operation is permissible the 4 exter-

nal components may be g5% tolerance including the

power supply

TLH10409 – 11

Note D

VI e (Applied Force) and can be Linearized (if necessary) in Software

FIGURE 9 Ratiometric Strain Gage SensoreController

TLH10409 – 12

Applications

Beverage BrewersDispensers

Ramp Current e IR e VCC a

R1 a R2

J 1R

Chemical Solution Control

Automatic Liquid Mixing Control

VI e

RX a RB

J VCCa

Ramp Time e VI

CHI

J e RX

RX a RB

J1aR2R

JCHR3J

FIGURE 10

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