MLX90314_12 Datasheet, PDF (10/28 Pages) Melexis Microelectronic Systems – Programmable Sensor Interface

MLX90314
Programmable Sensor Interface
Digital Features
Microprocessor, LX11 Core, Interrupt
Controller, Memories
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.
The LX11 microcontroller core is described in its own _{Watch Dog}
datasheet. As an overview, this implementation of the
LX11 RISC core has following resources:
An internal watch dog will reset the whole circuit in
case of a software crash. If the watch dog counter is
Two accumulators, one index and two interrupt
accumulators.
15 - 8 bit I/O ports to internal resources.
not reset at least once every 26 milliseconds (@ 2.46
MHz main clock), the microcontroller and all the
peripherals will be reset.
64 byte RAM.
4 kbytes ROM : 3 kbytes is available for the
Firmware
customer's application firmware. 1k is
reserved for test.
48 x 8 bit EEPROM.
Four interrupt sources, two UART interrupts
and two timers.
The MLX90314 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
UART
analog capabilities plus up to five different gain values
based on the input signal level. Also available in both
The serial link is a potentially full-duplex UART. It is ^{modes is the capability of range limiting and level}
receive-buffered, in that it can receive a second byte ^steering.
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 Temperature Processing
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.
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
Sending Data
temperature sensor. The filter equation is:
Writing a byte to port 1 automatically starts a
transmission sequence. The TX Interrupt is set when ^{If measured_temp > Temp_f(n) then}
the STOP-bit of the byte is latched on the serial line.
Temp_f(n+1) = Temp_f(n) + [measured_temp -
Temp_f(n)] / [2 ^n_factor].
Receiving Data
If measured_temp < Temp_f(n), then
Reception is initialized by a 1 to 0 transition on the ^{Temp_f(n+1) = Temp_f(n) - [measured_temp -}
serial line (i.e., a START-bit). The baud rate period ^{Temp_f(n)] [2 n_factor].}
(i.e., the duration of one bit) is divided into 16 phases. Temp_f(n+1) = new filtered temperature value.
The first six and last seven phases of a bit are not Temp_f(n) = previous filtered temperature value.
used. The decision on the bit-value is then the result of Measured_temp = Value from temperature A to D.
a majority vote of phase 7, 8 and 9 (i.e., the center of N_factor = Filter value set by the user (four
the bit).
LSB’s of byte 25 of EEPROM), range 0-6.
Spike synchronization is avoided by de-bouncing on _{The filtered temperature value, Temp_f, is stored in}
the incoming data and a verification of the START-bit _{RAM bytes 58 and 59. The data is a 10 bit value, left}
value. The RX Interrupt is set when the stop bit is _{justified in a 16 bit field.}
latched in the UART.
3901090314
Rev 008
Page 10
Apr/12