A96G140/A96G148/A96A148 User’s manual
15. USI
171
Both master and slave operation
Bus busy detection
15.14
USIn I2C bit transfer
The data on the SDAn line must be stable during HIGH period of the clock, SCLn. The HIGH or LOW
state of the data line can only change when the clock signal on the SCLn line is LOW. The exceptions
are START(S), repeated START(Sr) and STOP(P) condition where data line changes when clock line
is high.
Figure 94. Bit Transfer on the I2C-Bus (USIn)
15.15
USIn I2C start/ repeated start/ stop
One master can issue a START (S) condition to notice other devices connected to the SCLn, SDAn
lines that it will use the bus. A STOP (P) condition is generated by the master to release the bus lines
so that other devices can use it.
A high to low transition on the SDAn line while SCLn is high defines a START (S) condition.
A low to high transition on the SDAn line while SCLn is high defines a STOP (P) condition.
START and STOP conditions are always generated by the master. The bus is considered to be busy
after START condition. The bus is considered to be free again after STOP condition, i.e., the bus is
busy between START and STOP condition. If a repeated START condition (Sr) is generated instead of
STOP condition, the bus stays busy. So, the START and repeated START conditions are functionally
identical.
SCLn
SDAn
Data line Stable:
Data valid
except S, Sr, P
Change of Data
allowed