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transaction complete, a stop condition follows the NACK and completes the transaction. This
resets the sensor's I2C system preparing the sensor for a new I2C request.
Sensor Busy & NACK
The sensor may not be able to answer I2C requests when calculating measurements, processing
non-volatile memory and possibly other functions. If requests to the sensor are made when it is
busy, the input buffer will overflow and an error will occur. To prevent this potential error, the
sensor uses NACK functionality. NACK is generated automatically when a request is made to the
sensor and it busy and can not answer. Prior to making requests to the sensor, it is
recommended that the master (user controller) use the sensors NACK feature to determine if the
sensor is busy. If the sensor is addressed and responds with ACK, it is ready for a request; if NACK
is returned, the master should wait. A loop can be setup and continuous tests made until ACK is
returned.
I2C Timing
I2C timing conditions are shown below. Timing listed in the table are preliminary.
Symbol
Parameter
f
Clock frequency (max)
SCL
t
Stop bit to buss free time
BUFF
t
Hold time after start condition
HD.STA
t
Data setup time
SU.DAT
t
Low Ppriod of the clock (min)
LOW
t
High period of the clock (min)
HIGH
t
Data hold time
HD.DAT
t
Setup time for repeated start condition
SU.STA
t
Hold time for repeated clock
HD.STA
t
Rise time (max)
r
t
Fall time
f
t
Pulse width of spikes that must be suppressed
SP
t
Setup time for stop condition
SU.STO
Figure 6 - Timing Values & Recommended Conditions
In addition to I2C timing specifications, the sensor requires time to process instructions. To
accommodate this, the user must design in the required time. These are discussed later in the
document.
DOC: SPII2CHDWBrief - V2.71 07/25/2017
Figure 5 - Timing Diagram
Value
100kHz
5µs
5µs
5 µs
10µs
10µs
5µs
5µs
5µs
1µs
300ns
5µs
5µs
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