mlx90323 Melexis Company, mlx90323 Datasheet - Page 10

• Manufacturer Part Number: mlx90323
• Description: 4 ? 20 Ma Loop Sensor Interface With Signal Conditioning And Eeprom
• Manufacturer: Melexis Company

Temperature Sense
The temperature measurement, TPO, is generated from the external or internal temperature sensor. This is
converted to a 10-bit number for use in calculating the signal compensation factors. A 2-bit coarse adjustment
GNTP[1:0] is used for the temperature signal gain & offset adjustment.
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.
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.
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.
Temperature Processing
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:
3901090323
Rev 001
15 - 8 bit I/O ports to internal resources.
64 byte RAM.
4 kbytes ROM : 3 kbytes is available for customer's application firmware. 1k is reserved for test.
48 x 8 bit EEPROM.
7.3 Digital features
If measured_temp > Temp_f(n) then
If measured_temp < Temp_f(n), then
Temp_f(n+1) = Temp_f(n) + [measured_temp - Temp_f(n)] / [2
Page 10 of 24
with Signal Conditioning and EEPROM
4 – 20 mA Loop Sensor Interface
n_factor
MLX90323
]
Data Sheet
March/08