Optii FAQs

Spikes on the I2C signals

Spikes on the I2C signals
  • Lower serial resistances (low signals of external devices should clearly fall below the reference voltage Uref)
  • Increase the value of pull-up resistors Rp

I2C signals are not transmitted properly to the other bus

I2C signals are not transmitted properly to the other bus: Too small signal width, e.g. SCL signals do not arise up to the supply voltage Vcc
  • Bus capacitance is too high
  • Lower pull-up resistors (considering the difficulty with serial resistances)

I2C signals are not transmitted to the other bus

I2C signals are not transmitted to the other bus
The external device is not able to pull down the lines(s) lower than the reference voltage Uref.

  • Serial resistances on the bus are too high
  • The pull-up resistors are too low
Figure 1 shows a simplified schematic of the I2C bus (only SCL shown). Assuming Tracii XL 2.0 pulls down the line as an external device, the serial resistor Rs and the pull-up resistor Rp work as a voltage divider. A high value of Rs results in a high remaining voltage U2. If this voltage U2 does not fall below Uref, Optii is not able to detect the active device.For proper operation, a serial resistance Rs of 0 Ohm would be the best. If a decrease of the serial resistance is impossible, increasing the pull-up resistor Rp will also enhance the situation, but may limit the maximum transfer speed.

Figure 1 Problem of Serial Resistances

I2C lines are permanently low without any active external device

I2C lines are permanently low without any active external device and the I2C lines are high if Optii is not connected?
Please check this:

  • Are both sides powered with a voltage between 1.5 V and 5.5 V?
  • Do both buses deliver the required supply current?
  • Is the pinning of the cables correct?
  • Are the connectors plugged in correctly?