27.5.1 Control A

Name: CTRLA
Offset: 0x00
Reset: 0x00
Property: -

Bit 76543210 
  INPUTLVL SDASETUPSDAHOLD[1:0]FMPEN  
Access R/WR/WR/WR/WR/W 
Reset 00000 

Bit 6 – INPUTLVL Input Voltage Transition Level

This bit selects between I2C and SMBUS.
ValueNameDescription
0 I2C I2C input voltage transition level
1 SMBUS SMBus 3.0 input voltage transition level

Bit 4 – SDASETUP SDA Setup Time

This bit is used in TWI Client mode to select the clock hold time and to ensure the minimum setup time on the SDA out signal.

ValueNameDescription
0 4CYC SDA setup time is four clock cycles
1 8CYC SDA setup time is eight clock cycles

Bits 3:2 – SDAHOLD[1:0] SDA Hold Time

This bit field selects the SDA hold time for the TWI. See the Electrical Characteristics section for details.

ValueNameDescription
0x0 OFF Hold time OFF
0x1 50NS Short hold time
0x2 300NS Meets the SMBus 2.0 specifications under typical conditions
0x3 500NS Meets the SMBus 2.0 across all corners

Bit 1 – FMPEN FM Plus Enable

Writing a ‘1’ to this bit selects the 1 MHz bus speed for the TWI in default configuration or the TWI host in Dual mode configuration.

ValueNameDescription
0 OFF Operating in Standard mode or Fast mode
1 ON Operating in Fast mode Plus