MLX90308CCC datasheet(10/26 Pages) MICRO-ELECTRONICS

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MLX90308CCC

Programmable Sensor Interface

MLX90308CCC Programmable Sensor Interface

Page 10

Rev 2.2

23/Oct/01

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

lev el

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].

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.

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.

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.

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