MLX90314 Datasheet, PDF (10/26 Pages) List of Unclassifed Manufacturers – Programmable Sensor Interface

MLX90314AB
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.
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.
Firmware
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 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].
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.
MLX90314AB Programmable Sensor Interface
Page 10
Rev 2.2
23/Oct/01