Texas Instruments MSP430x4xx - Manual (Page 492)

Scan IF Operation
24-32 Scan IF
24.2.7 Using the Scan IF With Resistive Sensors
Systems with GMRs use magnets on an impeller to measure rotation. The
damping material and magnets modify the electrical behavior of the sensor so
that rotation and direction can be detected.
Rotation is measured with resistive sensors by connecting the resistor dividers
to ground for a short time allowing current flow through the dividers. The
resistors are affected by the rotating disc creating different divider voltages.
The divider voltages are sampled with the sample-and-hold circuits. After the
signals have settled the dividers may be switched off to prevent current flow
and reduce power consumption. The DAC is used to set the reference level
for the comparator, and the comparator detects if the sampled voltage is above
or below the reference level. If the sampled voltage is above the reference
level the comparator output is high. Figure 24−18 shows the connection for
resistive sensors.
Figure 24−18. Resistive Sensor Connections
Power
Supply
Terminals
SIFCI0
SIFCI
SIFCI1
SIFCI2
SIFCI3
470 nF
AV
CC
DV
CC
DV
SS
AV
SS
SIFVSS
SIFCOM
SIFCH1
SIFCH0
SIFCH2
SIFCH3