mlx90323 Melexis Company, mlx90323 Datasheet - Page 13

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

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.
3901090323
Rev 001
Table 4. Examples of Fixed Point Signed
Numbers
Decimal
Value
0
1023
1024
2047
2048
3071
Hexadecimal
Equivalent
0000h
3FFh
400h
7FFh
800h
0BFFh
Page 13 of 24
with Signal Conditioning and EEPROM
4 – 20 mA Loop Sensor Interface
Fixed Point
Signed Number
Equivalent
+0.00
+0.9990234
+1.000
+1.9990234
-0.000
-0.9990234
MLX90323
Data Sheet
March/08