MLX90323 Datasheet, PDF (11/25 Pages) Melexis Microelectronic Systems – 4 – 20 mA Loop Sensor Interface with Signal Conditioning and EEPROM

MLX90323
4 – 20 mA Loop Sensor Interface
with Signal Conditioning and EEPROM
7.5 Communications
The MLX90323 firmware transfers a complete byte of data into and from the memory based on a simple
command structure. The commands allow data to be read and written to and from the EEPROM and read
from the RAM. RAM data that can be read includes the current digitized temperature. The commands are
described below. Melexis provides setup software for programming the MLX90323.
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. UART configuration: start bit, 8 data bits, stop bit.
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:
Command
Read RAM
Write RAM
Read EEPROM
Write EEPROM
Reset
Start
Stop
bit
Bit7 Bit6 Bit5 Bit4 Bit3 Bit2 Bit1 Bit0 Bit
0 1 1 AD5 AD4 AD3 AD2 AD1 AD0
1
0 0 0 AD5 AD4 AD3 AD2 AD1 AD0
1
0 1 0 AD5 AD4 AD3 AD2 AD1 AD0
1
0 0 1 AD5 AD4 AD3 AD2 AD1 AD0
1
010 1 1 1 1 1 1
1
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 MLX90323. 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.
3901090323
Rev 003
Page 11 of 25
Data Sheet
Feb/12