FTDI Community

General Category => Discussion - Hardware => Topic started by: GHOC3D on March 05, 2021, 08:24:10 PM

Title: FT2232H default state of unused/GPIO pins when using a channel as JTAG, I2C, etc
Post by: GHOC3D on March 05, 2021, 08:24:10 PM

Hello,

I have a design that is using an FT2232H with channel A configured as JTAG, and channel B configured as I2C. On the JTAG channel, I wish to use one of the free pins as a GPIO to reset my board. I have looked through AN_184, table 5.1, and I see that, for example, the ACBUS1 pin is designated as 'Function' when the device is enumerated/active. But before any software intervention, what is the initial state of this pin? Is it driving high, driving low, or is it an input with pull-up/down? If it is pulled up or down, what is the resistance value?

My hope is that the GPIO pin is tristated initially, so I can pull it up or down on my PCB such that my reset signal is held inactive.

Thank you.

Title: Re: FT2232H default state of unused/GPIO pins when using a channel as JTAG, I2C, etc
Post by: FTDI Community on March 09, 2021, 04:39:58 PM

Hello,

The FT2232H ports will default to Async serial mode (UART) so you can check Table 3.1 FT2232H Pin Configurations for 64-pin QFN and LQFP package in the FT2232H Datasheet (https://ftdichip.com/wp-content/uploads/2020/07/DS_FT2232H.pdf) for the default pin functions.

Pins marked ** default to tri-stated inputs with an internal 75KΩ (approx.) pull up resistor to VCCIO.
This is the case for ACBUS1 that you mentioned.

Best Regards,
FTDI Community

Title: Re: FT2232H default state of unused/GPIO pins when using a channel as JTAG, I2C, etc
Post by: GHOC3D on March 09, 2021, 05:56:46 PM

Thank you for that answer, that's good news!

If I then start to use the MPSSE as JTAG, without having done anything to alter the state of ACBUS1, which becomes GPIOH1, will GPIOH1's state still remain a tri-stated input with internal 75KR pullup until I change it to something else?

Title: Re: FT2232H default state of unused/GPIO pins when using a channel as JTAG, I2C, etc
Post by: FTDI Community on March 11, 2021, 04:51:53 PM

Hello,

Yes this will be the default pin configuration until you enable MPSSE mode.

We have development modules available for test, evaluation and reference:

FT2232H-56 Mini-Module (https://ftdichip.com/products/ft2232h-56-mini-module/)
FT2232H Mini-Module (https://ftdichip.com/products/ft2232h-mini-module/)

The -56 module is easier to power with a single jumper in comparison to the other modules which needs multiple external connections to power it.

Best Regards,
FTDI Community

Title: Re: FT2232H default state of unused/GPIO pins when using a channel as JTAG, I2C, etc
Post by: GHOC3D on March 12, 2021, 01:21:21 AM

Thank you, that works for me.