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Author Topic: FT51A output pad configuration  (Read 71 times)

YOZHik

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FT51A output pad configuration
« 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 );
« Last Edit: October 10, 2017, 06:51:01 PM by YOZHik »
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FTDI Community

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Re: FT51A output pad configuration
« Reply #1 on: October 11, 2017, 11:24:38 AM »

Hello,

All our software examples 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
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YOZHik

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Re: FT51A output pad configuration
« Reply #2 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.
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