MLX90614 family
Single and Dual Zone
Infra Red Thermometer in TO-39
8.4.2 Differences with the standard SMBus specification (reference [1])
There are eleven command protocols for standard SMBus interface. The MLX90614 supports only two of
them. Not supported commands are:
•
•
•
•
Quick Command
Byte commands - Sent Byte, Receive Byte, Write Byte and Read Byte
Process Call
Block commands – Block Write and Write-Block Read Process Call
Supported commands are:
•
•
Read Word
Write Word
8.4.3 Detailed description
The PWM/SDA pin of MLX90614 can operate also as PWM output, depending on the EEPROM settings. If
PWM is enabled, after POR the PWM/SDA pin is directly configured as PWM output. The PWM mode can be
avoided and the pin can be restored to its Data function by a special command. That is why hereafter both
modes are treated separately.
8.4.3.1 Bus Protocol
1
7
1
1
8
1
1
S
Slave Address
Wr A
Data Byte
A
P
S
Sr
Start Condition
Repeated Start Condition
Read (bit value of 1)
Write (bit value of 0)
Rd
Wr
A
Acknowledge (this bit can be 0 for ACK and 1 for NACK)
S
Stop Condition
PEC
Packet Error Code
Master-to-Slave
Slave-to-Master
Figure 4: SMBus packet element key
After every 8 bits received by the SD an ACK/NACK takes place. When a MD initiates communication, it first
sends the address of the slave and only the SD which recognizes the address will ACK, the rest will remain
silent. In case the SD NACKs one of the bytes, the MD should stop the communication and repeat the
message. A NACK could be received after the PEC. This means that there is an error in the received
message and the MD should try sending the message again. The PEC calculation includes all bits except the
START, REPEATED START, STOP, ACK, and NACK bits. The PEC is a CRC-8 with polynomial
X8+X2+X1+1. The Most Significant Bit of every byte is transferred first.
3901090614
Rev 003
Page 14 of 40
Data Sheet
03/Oct/2007
MELEXIS [ Melexis Microelectronic Systems ]
