I created a MCU-based circuit and have used it successfully to initialized the M96C46 EEPROM via a card edge connector. Referring to the attached schematic to do this, my MCU holds the hub in reset via J6E, and drives J6K (chip select), as well as the clock and data signals. Then I disconnected this MCU circuit and connected the hub directly to a USB port on a Windows PC.
Since the hub datasheet suggested 100µsec to 1ms reset time, I’ve measured R2/C5 hub reset voltage levels to be < 0.8 Vdc (Vil max) asserted for 200µsec, and reset reaches Vih min (~1.8V) at about 800µsec from a “brick wall” rise time for the 3.3Vdc rail. Note that the 3.3V rail is created by a LDO with Vbus for Vin. and the C4 & C11 bypass caps are not installed contrary to the schematic. However, with this reset timing, the hub doesn’t communicate with the EEPROM, but does operate properly other than reporting the incorrect VID = 0x0000 and PID = 0x0000 to Windows Device Manager. Presumably the hub is configured as “ganged” overcurrent protection (at EEPROM address 0x0000) since this is what was reported for the VID/PID. EEPROM datasheet for reference https://www.st.com/resource/en/datasheet/m93c46-w.pdf
I changed R2 from 10K to 100K, and observed EEPROM communications about 6.7ms after the "brick wall" 3.3V power supply comes up. Device Manager reports the hub VID/PID that I had previously written into the EEPROM with my MCU circuit.
But I’m also concerned about having too long of a reset from an EEPROM communications perspective as well (in addition to too short). I also tried R2 = 100K and C5 = 1µF which resulted in the correct VID/PID. However, I’ve twice observed the correct initialized VID, but 0x0000 for the PID upon virgin power-up on two different units. Both units seemed to report the correct VID / PID on subsequent disconnect / reconnect events.
So there appears to be a critical timing window for EEPROM communication, and tradeoffs between hub USB response time and EEPROM communication; I’m concerned about reliability.
Schematic Can you offer any insight and guidance?