MLX90308(2004) Просмотр технического описания (PDF) - Melexis Microelectronic Systems

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MLX90308
(Rev.:2004)

Programmable Sensor Interface

Melexis Microelectronic Systems  

MLX90308

Programmable Sensor Interface

Digital Features

Microprocessor, LX11 Core, Interrupt

Controller, Memories

The LX11 microcontroller core is described in its own

datasheet. As an overview, this implementation of the

LX11 RISC core has following resources:

Two accumulators, one index and two interrupt

accumulators.

15 - 8 bit I/O ports to internal resources.

64 byte RAM.

4 kbytes ROM : 3 kbytes is available for the

customer's application firmware. 1k is

reserved for test.

48 x 8 bit EEPROM.

Four interrupt sources, two UART interrupts

and two timers.

UART

The serial link is a potentially full-duplex UART. It is

receive-buffered, in that it can receive a second byte

before a previously received byte has been read from

the receiving register. However, if the first byte is not

read by the time the reception of the second byte is

completed, the first byte will be lost. The UART's baud

rate depends on the RC-oscillator's frequency and the

"TURBO"-bit (see output port). Transmitted and

received data has the following structure: start bit = 0,

8 bits of data, stop bit = 1.

Sending Data

Writing a byte to port 1 automatically starts a

transmission sequence. The TX Interrupt is set when

the STOP-bit of the byte is latched on the serial line.

Timer

The clock of the timers TMI and TPI is taken directly

from the main oscillator. The timers are never

reloaded, so the next interrupt will take place 2x

oscillator pulses after the first interrupt.

Watch Dog

An internal watch dog will reset the whole circuit in

case of a software crash. If the watch dog counter is

not reset at least once every 26 milliseconds (@ 2.46

MHz main clock), the microcontroller and all the

peripherals will be reset.

Firmware

The MLX90308 firmware performs the signal

conditioning by either of two means: analog or digital.

The analog signal conditioning allows separate offset

and gain temperature coefficients for up to four

temperature ranges. Digital mode allows for all of the

analog capabilities plus up to five different gain values

based on the input signal level. Also available in both

modes is the capability of range limiting and level

steering.

.

Temperature Processing

In both analog and digital modes, the temperature

reading controls the temperature compensation. This

temperature reading is filtered as designated by the

user. The filter adjusts the temperature reading by

factoring in a portion of the previous value. This helps

to minimize the effect of noise when using an external

temperature sensor. The filter equation is:

If measured_temp > Temp_f(n) then

Temp_f(n+1) = Temp_f(n) + [measured_temp -

Temp_f(n)] / [2 n_factor].

Receiving Data

Reception is initialized by a 1 to 0 transition on the

serial line (i.e., a START-bit). The baud rate period

(i.e., the duration of one bit) is divided into 16 phases.

The first six and last seven phases of a bit are not

used. The decision on the bit-value is then the result of

a majority vote of phase 7, 8 and 9 (i.e., the center of

the bit).

Spike synchronization is avoided by de-bouncing on

the incoming data and a verification of the START-bit

value. The RX Interrupt is set when the stop bit is

latched in the UART.

If measured_temp < Temp_f(n), then

Temp_f(n+1) = Temp_f(n) - [measured_temp -

Temp_f(n)] [2 n_factor].

Temp_f(n+1) = new filtered temperature value.

Temp_f(n) = previous filtered temperature value.

Measured_temp = Value from temperature A to D.

N_factor = Filter value set by the user (four

LSB’s of byte 25 of EEPROM), range 0-6.

The filtered temperature value, Temp_f, is stored in

RAM bytes 58 and 59. The data is a 10 bit value, left

justified in a 16 bit field.

3901090308

Rev 006

Page 10

Apr/04

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