MLX90314_12 Datasheet, PDF (15/28 Pages) Melexis Microelectronic Systems – Programmable Sensor Interface

MLX90314
Programmable Sensor Interface
UART Commands
The commands can be divided into three parts: (1)
downloading of data from the ASIC, (2) uploading of
data to the ASIC and (3) the reset command.
All the commands have the same identification bits.
The two MSB’s of the sent byte indicate the command
while the last six MSB’s designate the desired
address. The commands are coded as followed:
11 to read a RAM byte.
10 to read an EEPROM byte.
01 to write in the EEPROM.
00 to write in the RAM.
The addresses can include 0-63 for the RAM, 0-47 for
the EEPROM, and 63 for the EEPROM, RESET
Command (read).
Downloading Command
With one byte, data can be downloaded from the
ASIC. The ASIC will automatically send the value of
the desired byte.
Uploading Command
Writing to the RAM or EEPROM involves a simple
handshaking protocol in which each byte transmitted
is acknowledged by the firmware. The first byte
transmitted to the firmware includes both command
and address. The firmware acknowledges receipt of
the command and address byte by echoing the same
information back to the transmitter. This “echo” also
indicates that the firmware is ready to receive the byte
of data to be stored in RAM or EEPROM. Next, the
byte of value to be stored is transmitted and, if
successfully received and stored by the firmware, is
acknowledged by a “data received signal,” which is
two bytes of value BCh. If the “data received signal” is
not observed, it may be assumed that no value has
been stored in RAM or EEPROM.
Reset Command
Reading the address 63 of the EEPROM resets the
ASIC and generates a received receipt indication.
Immediately before reset, the ASIC sends a value of
BCh to the UART, indicating that the reset has been
received.
EEPROM Data
All user-settable variables are stored in the EEPROM
within the MLX90314. The EEPROM is always re-
programmable. Changes to data in the EEPROM do
not take effect until the device is reset via a soft reset
or power cycle. 12 bit variables are stored on 1.5
bytes. The 4 MSB’s are stored in a separate byte and
shared with the four MSB’s of another 12-bit variable.
Clock Temperature Stabilization
To provide a stable clock frequency from the internal
clock over the entire operating temperature range,
three separate clock adjust values are used. Shifts in
operating frequency over temperature do not effect the
performance but do, however, cause the
communications baud rate to change.
The firmware monitors the internal temperature sensor
to determine which of three temperature ranges the
device currently is in. Each temperature range has a
factory set clock adjust value, ClkTC1, ClkTC2, and
ClkTC3. The temperature ranges are also factory set.
The Ctemp1 and Ctemp2 values differentiate the three
ranges. In order for the temperature A to D value to be
scaled consistently with what was used during factory
programming, the CLKgntp (temperature amplifier
gain) valued is stored. The Cadj value stored in byte 1
of the EEPROM is used to control the internal clock
frequency while the chip boots.
Unused Bytes
There are eight unused bytes in the EEPROM address
map. These bytes can be used by the user to store
information such as a serial number, assembly date
code, production line, etc. Melexis doesn’t guarantee
that these bytes will be available to the user in future
revisions of the firmware.
EEPROM Checksum
A checksum test is used to ensure the contents of the
EEPROM. The eight bit sum of all of the EEPROM
addresses should have a remainder of 0FFh when the
checksum test is enabled (mode byte). Byte 47 is
used to make the sum remainder totals 0FFh. If the
checksum test fails, the output will be driven to a user
defined value, Faultval. When the checksum test is
enabled, the checksum is verified at initialization of
RAM after a reset.
RAM Data
All the coefficients (pressure, temperature) are
compacted in a manner similar to that used for the
EEPROM. They are stored on 12 bits (instead of
keeping 16 bits for each coefficient). All the
measurements are stored on 16 bits. The user must
have access to the RAM and the EEPROM, while
interrupt reading of the serial port. Therefore, bytes
must be kept available for the return address, the A-
accu and the B-accu, when an interrupt occurs. The
RAM keeps the same structure in the both modes.
3901090314
Rev 008
Page 15
Apr/12