MAX132 Maxim, MAX132 Datasheet - Page 15

• Manufacturer Part Number: MAX132
• Description: 18-Bit ADC with Serial Interface
• Manufacturer: Maxim

of the overall accuracy of the current source. The cur-
rent source delivers 2mA, resulting in about 500mV
across the 250Ω resistor—suitable to fit the MAX132’s
±512mV full-scale range. Note that the accuracy of the
reference resistor (0.1%) sets the circuit’s accuracy.
The power consumption of the RTD sensor is small
(0.5mW), minimizing errors caused by self-heating.
Figure 12 shows a high-level software subroutine for
reading output/status data and writing command data
Figure 11. Ratiometric Configuration Using the Differential Reference Inputs
SPI is a trademark of Motorola, Inc. Microwire is a trademark of National Semiconductor Corp.
PT100
RTD
Interfacing to a µP Parallel Port
______________________________________________________________________________________
MAX872
GND
V
IN
IC1
S
+5V
OUT
RW1
RW2
V
R
4.096V
250
0.1%
2k
±18-Bit ADC with Serial Interface
INTERFACE
SERIAL-
DATA
CHIP SELECT
DATA OUT
DATA IN
CLOCK
0.1 F
to the MAX132. It provides an algorithm for serial com-
munication when the µP port does not have a prede-
fined serial interface protocol (i.e., SPI™ or Microwire™).
The routine sends command data (TxByte) to the
MAX132 while concurrently collecting the MAX132’s
output register data (selected by the previous write
cycle). Note that a write is required before each read to
change the next output register to be read, and that
the subroutine must be repeated three times to read
the output status register, Output Register 0, and
Output Register 1.
11
10
14
15
1
2
3
4
7
8
9
CS
DIN
DOUT
SCLK
EOC
PG0
PG1
PG2
PG3
IN HI
IN LO
10 F
-5V
13
12
DGND
V-
MAX132
IC2
AGND
V+
24
BUF OUT
10 F
+5V
INT OUT
REF+ IN
16
REF- IN
CREF+
RW1, RW2 WIRE RESISTANCE
CREF-
INT IN
OSC2
OSC1
23
22
21
19
20
18
17
5
6
32,768Hz
600k
4.7nF
0.1 F
0.1 F
15