SLUA475 November   2016 BQ2060A , BQ20Z80 , BQ40Z50-R1 , BQ40Z50-R2 , BQ40Z60 , BQ78350-R1 , BQ78350-R1A

 

  1.   SMBus Made Simple
    1.     Trademarks
    2. 1 Getting to Know SMBus
      1. 1.1 Closer Inspection
      2. 1.2 Final Considerations
        1. 1.2.1 Clock Stretching
        2. 1.2.2 Broadcasting (Master Mode Messages)
        3. 1.2.3 PEC
          1. 1.2.3.1 How to Calculate PEC
        4. 1.2.4 Examples
          1. 1.2.4.1 Example 1
          2. 1.2.4.2 Example 2
          3. 1.2.4.3 Example 3
          4. 1.2.4.4 Example 4
    3. 2 Most Common Problems
    4. 3 Glossary
    5. 4 References
  2.   A SMBus Reference Sheet
    1.     19

1.2.1 Clock Stretching

clk_str_lua475.gifFigure 3. SMBus Clock Stretch

Clock stretching is a simple way for the slave to indicate to the host that it is busy (see Figure 3). Any time the clock is low in the packet, the slave has the right to grab the clock and hold it low as long as required; however, the bit must not cause a packet timeout (25 ms).

The entire packet must not be longer than 25 ms, which includes the clock stretch. TI fuel gauges usually only clock stretch before or after the ACK or NACK bits.