MLX90614 family
Single and Dual Zone
Infra Red Thermometer in TO-39
3901090614
Page 13 of 40
Data Sheet
Rev 003
03/Oct/2007
8.3.4 RAM
It is not possible to write into the RAM memory. It can only be read and only a limited number of RAM
registers are of interest to the customer.
RAM (32x17)
Name
Address
Read access
Melexis reserved
000h
Yes
…
…
…
Melexis reserved
005h
Yes
TA
006h
Yes
TOBJ1
007h
Yes
TOBJ2
008h
Yes
Melexis reserved
009h
Yes
…
…
…
Melexis reserved
01Fh
Yes
8.4 SMBus compatible 2-wire protocol
The chip supports a 2 wires serial protocol, build with pins PWM/SDA and SCL.
•
SCL – digital input, used as the clock for SMBus compatible communication. This pin has the
auxiliary function for building an external voltage regulator. When the external voltage regulator is
used, the 2-wire protocol is available only if the power supply regulator is overdriven.
•
PWM/SDA – Digital input/output, used for both the PWM output of the measured object
temperature(s) or the digital input/output for the SMBus. The pin can be programmed in EEPROM to
operate as Push/Pull or open drain NMOS (open drain NMOS is factory default). In SMBus mode
SDA is forced to open drain NMOS I/O, push-pull selection bit defines PWM/Thermal relay operation.
8.4.1 Functional description
The SMBus interface is a 2-wire protocol, allowing communication between the Master Device (MD) and one
or more Slave Devices (SD). In the system only one master can be presented at any given time [1]. The
MLX90614 can only be used as a slave device.
Generally, the MD initiates the start of data transfer by selecting a SD through the Slave Address (SA).
The MD has read access to the RAM and EEPROM and write access to 9 EEPROM cells (at addresses
0x20h, 0x21h, 0x22h, 0x23h, 0x24h, 0x25h*, 0x2Eh, 0x2Fh, 0x39h). If the access to the MLX90614 is a read
operation it will respond with 16 data bits and 8 bit PEC only if its own slave address, programmed in internal
EEPROM, is equal to the SA, sent by the master. The SA feature allows connecting up to 127 devices with
only 2 wires, unless the system has some of the specific features described in paragraph 5.2 of reference
[1]. In order to provide access to any device or to assign an address to a SD before it is connected to the bus
system, the communication must start with zero SA followed by low RWB bit. When this command is sent
from the MD, the MLX90614 will always respond and will ignore the internal chip code information.
Special care must be taken not to put two MLX90614 devices with the same SD addresses on the
same bus as MLX90614 does not support ARP[1].
The MD can force the MLX90614 into low consumption mode “sleep mode” (3V version only).
Read flags like “EEBUSY” (1 – EEPROM is busy with executing the previous write/erase), “EE_DEAD” (1 –
there is fatal EEPROM error and this chip is not functional**).
Note*: This address is readable and writable. Bit 3 should not be altered as this will cancel the factory
calibration.
Note**: EEPROM error signaling is implemented in automotive grade parts only.
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