DA6502.008

29 November 2012

6 (20)

OPERATING MODES

MAS6502 has two operating modes, pressure and

temperature measurement mode. In the pressure

mode

the

pressure

dependent sensor bridge

voltage is connected to the ADC input. In the

temperature

measurement

mode

the

resistive

sensor is connected into a Wheatstone resistor

bridge circuit together with four internal resistors

(see Temperature Measurement Configuration in

the

Application

Information

chapter)

and

the

temperature dependent bridge output voltage is

connected to the ADC input.

Switching

between

pressure

and

temperature

measurement modes is done via the single ADC

control register. The measurement configuration

includes selection of over sampling ratio, input

signal range, offset and sensor resistance. By

writing an 8-bit configuration data to the ADC

control register a new A/D conversion is started.

See further details in the ADC Control Register

chapter.

MAS6502 includes a 256-bit EEPROM memory for

storing trimming and calibration data on chip. The

first 8-bits of EEPROM are reserved for internal

oscillator trimming but the remaining 248-bits are

free for calibration and other data.

The stored calibration data should comprise of

calibration

and

temperature

compensation

coefficients which can be used to calculate accurate

calibrated pressure and temperature measurement

results

from

the

non-calibrated

measurement

results. All calculations need to be done in the

external micro controller unit (MCU).

A calibrated MAS6502 sensor system is operated

as illustrated in figure 2. The calibration and

compensation coefficients need to be read to the

MCU memory only once. From each pair of

pressure and temperature measurements results

the accurate pressure and temperature values are

then calculated by using the external MCU.

All communication with MAS6502 is done using the

bi-directional I

Starting an A/D conversion, reading out the

conversion result and reading and writing data from

and to the EEPROM memory are all accomplished

via serial bus communication.

In addition to the I

includes also end-of-conversion (EOC) and master

reset (XCLR) pins. See A/D Conversion in the Serial

Data Interface (I

Figure 2. Flow chart for a calibrated MAS6502 sensor system

START

READ EEPROM

CALIBRATION DATA

MEASURE PRESSURE

MEASURE TEMPERATURE

CALCULATE CALIBRATED

TEMPERATURE

CALCULATE TEMPERATURE

COMPENSATED PRESSURE