Hi
Power Sequence
It is recommended that VCC, VCCIO and RESET# are set at the same time, I would suggest connecting RESET# and VCCIO to 3V3OUT as this will ensure these are set when VCC is powered.
Mixing a bus and self-powered design is not recommended. VCCIO should be connected to either 5V or 3.3V in one of the following configurations:
• Entirely bus powered, that is from the USB port (VCC and VCCIO pins). In the case where 3.3V IO's are required a local 3.3V regulator is needed which can be supplied from the USB bus. Alternatively, in some cases, where only a small amount of current is required (< 5mA), it may be possible to use the in-built regulator of the FTDI device (where available) to supply the 3.3V to VCCIO without any other components being required. In this case, connect VCCIO to the 3V3OUT pin of the FTDI device.
• Entirely self-powered, that is from the local supply on your board. In the case where 3.3V IO's are required, you will need 5V and 3.3V to be available on your board.
Crystal Frequency
Section 6.3 of the
FT2232H Datasheet gives an example of a 12MHz crystal being connected in the oscillator configuration.
Suspend State
You can read about USB Selective Suspend in AN_107
Advanced Driver Options.
We tell the system we're idle and the system puts us in a low power state.
If it is in selective suspend, the next request through the driver will bring it out of suspend.
For example, in a terminal emulator open port, no data for say 5 seconds will put the device into suspend. The next keystroke will generate a write request. When the driver receives that request, it will come out of suspend and send the data.
There is also an additional feature called remote wake-up which can be used to bring the device out of suspend mode:
RI# pin: Ring Indicator Control Input. When remote wake up is enabled in the internal EEPROM taking RI# low (20ms active low pulse) can be used to resume the PC USB host controller from suspend.
Suspend mode can be monitored via the SLEEP# pin.
please let us know f you have any other questions.
Best Regards
FTDI community