User Manual

Application Note
SMBus communication with MLX90614
390119061402 Page 6 of 32 Jan-2008
Rev 004
Note 3: t
HIGH,MAX
provides a simple guaranteed method for masters to detect bus idle conditions. A master can
assume that the bus is free if it detects that the clock and data signals have been high for greater than t
HIGH,MAX
.
Note 4: t
LOW:SEXT
is the cumulative time a given slave device is allowed to extend the clock cycles in one message
from the initial START to the STOP. It is possible that, another slave device or the master will also extend the clock
causing the combined clock low extend time to be greater than t
LOW:SEXT
. Therefore, this parameter is measured with
the slave device as the sole target of a full-speed master.
Note 5: t
LOW:MEXT
is the cumulative time a master device is allowed to extend its clock cycles within each byte of a
message as defined from START-to-ACK, ACK-to-ACK, or ACK-to-STOP. It is possible that a slave device or
another master will also extend the clock causing the combined clock low time to be greater than t
LOW:MEXT
on a
given byte. Therefore, this parameter is measured with a full speed slave device as the sole target of the master.
Note 6: Rise and fall time is defined as follows:
t
R
= (V
IL,MAX
- 0.15) to (V
IH,MIN
+ 0.15)
t
F
= (V
IH,MIN
+ 0.15)to (V
IL,MAX
- 0.15)
Note 7: For the first silicon revision of a MLX90614 module this value is above 500ns
4.4 Timeouts
Timeout measurement intervals illustrates the definition of the timeout intervals, t
LOW:SEXT
and t
LOW:MEXT
.
Fig.5: Timeout measurement intervals
4.5 Slave device timeout definitions and conditions
The t
TIMEOUT,MIN
parameter allows a master or slave to conclude that a defective device is holding
the clock low indefinitely or a master is intentionally trying to drive devices off the bus. It is highly
recommended that a slave device release the bus (stop driving the bus and let SCL and SDA
float high) when it detects any single clock held low longer than t
TIMEOUT,MIN
. Devices that have
detected this condition must reset their communication and be able to receive a new START
condition in no later than t
TIMEOUT,MAX
. Slave devices that violate t
LOW:SEXT
are not conformant with
this specification. A Master is allowed to abort the transaction in progress to any slave that
violates the t
LOW:SEXT
or t
TIMEOUT,MIN
specifications.