EVB90615 Datasheet, PDF (12/30 Pages) Melexis Microelectronic Systems – Infra Red Thermometer

8.4.3.1 Bus Protocol
MLX90615
Infra Red Thermometer
1
7
11
S Slave Address Wr A
8
Data Byte
11
AP
S
Sr
Rd
Wr
A
P
PEC
Start Condition
Repeated Start Condition
Read (bit value of 1)
Write (bit value of 0)
Acknowledge (this bit can be 0 for ACK and 1 for NACK)
Stop Condition
Packet Error Code
Master-to-Slave
Slave-to-Master
Figure 5: 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. If 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 transmitted first.
8.4.3.1.1 Read Word (depending on the command – RAM or EEPROM)
1
7
S Slave Address
11
Wr A
8
Command
11
7
11
A Sr Slave Address Rd A ………..
8
1
8
1
……….. Data Byte Low A Data Byte High A
Figure 6: SMBus read word format
8
PEC
11
AP
3901090615
Rev 001
Page 12 of 30
Data Sheet
28/Aug/2008