FTDI Community

General Category => Discussion - Software => Topic started by: YOZHik on October 10, 2017, 04:48:49 PM

Title: FT51A output pad configuration
Post by: YOZHik on October 10, 2017, 04:48:49 PM

Tried to configure a pin in output mode, but it failed to output unless configured with pull-up enabled (works with IOMUX_PAD_PULL_UP and doesn't work with IOMUX_PAD_PULL_NONE). Open-drain like-behaviour instead of push-pull? The Programming Guide (AN-289) states however that pull up/down bits take effect only if a pin is configured as input. Is that kind of behavior correct? Or may be I am doing something wrong?

Code: [Select]

IOMUX_OUTPUT( DIO_14, IOMUX_OUT_PORT3_6 );
IOMUX_set_pad_config( DIO_14, IOMUX_PAD_DRIVE_CURRENT_16MA, IOMUX_PAD_TRIGGER_NORMAL, IOMUX_PAD_SLEW_RATE_FAST, IOMUX_PAD_PULL_UP );

Title: Re: FT51A output pad configuration
Post by: FTDI Community on October 11, 2017, 11:24:38 AM

Hello,

All our  software examples (http://www.ftdichip.com/Support/SoftwareExamples/FT51A.htm) use the 8051 Digital I/O ports P1 and P3 or Analog I/O ports P0 and P2. The pull up/downs are only relevant to the pins when they are inputs, and like the 8051 the pins are open drain when set as outputs.

Also note that traditional 8051 Port 0 (P0) is open-collector, unlike the other ports (P1 to P3).
This means that an external pull-up is required when using P0 as GPIO for example.

Thanks,
FTDI Community

Title: Re: FT51A output pad configuration
Post by: YOZHik on October 11, 2017, 03:11:25 PM

Got it. But there is no direct mentioning of open drain IO pins either in the datasheet or the programming guide. Moreover, Voh "Output Voltage High" is defined in "Table 4-3 – IO Characteristics VCCIO = +3V3" making it look like the IO pins are push-pull with configurable drive strength. A bit confusing.