MLX90308CAB Datasheet, PDF (15/26 Pages) List of Unclassifed Manufacturers – Programmable Sensor Interface

MLX90308CAB
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 MLX90308CAB. 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
makes no 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.
MLLXX990023x0x8NCaAmBe oPfroSgernasmormable Sensor Interface RePvaYg.Xe 15
22/Aug/R98ev 3.0 21/MayP/0a1ge 15