Team,
We were able to capture some interesting waveforms, see attached.
I would like to draw your attention to the tabs “compare” and “zoom”. They show the communication between the SMBUS charger and the SMBUS smart battery. I am holding the host microcontroller in reset so that it doesn’t transmit anything. The “NO HOST” waveform indicates that I have removed the host and the TCA9406 from the bus. The “STM32_RESET” indicates that I have connected the TCA9406 to the bus but I am holding the host in reset. What you can see is that there are several bytes transmitted in “NO HOST” but only one byte transmitted in “STM32_RESET”. Upon closer inspection, there is no ACK bit in “STM32_RESET”. The ACK bit is shown in the “zoom” tab.
If I understand this right, the one shot edge accelerator circuit in the TCA9406 reduces the rise time of the data by an order of magnitude. I am not quite understanding why the slave device is not able to drive the data line low.
Could I get your thoughts?