writing to GPIO pins

[rdpoor]

I'm able to get my FT232RQ into bitbang mode and read pins using ftdi.read_pins(), but I can't find documentation (nor even source code) that shows how to write to the pins. I thought maybe I should be using ftdi.write_data(), but that doesn't appear to be having the desired effect:

Here's what I tried and what I observed:

>>> from pyftdi.ftdi import Ftdi
>>> ftdi = Ftdi()
>>> ftdi.open_bitbang_from_url('ftdi:///1', direction=0xff)    # declare GPIO pins as outputs
>>> ftdi.read_pins()
2
>>> ftdi.write_data([0x0])
> (invalid output byte sequence)
1
>>> ftdi.read_pins()
255

Since read_pins() now returns 255, it appears that write_data([0x0]) had some effect (despite the error message), but it did not produce visible effects in my FT232RQ: there are LEDs on two of the GPIO pins and they did not light up as I would expect them to.

The fundamental question remains: how do I write to the GPIO port in bitbang mode?

update

I should make it clear that I'm trying to access the 4-bit CBUS rather than the 8-bit I/O bus.

[rdpoor]

To make it clear, here's a minimal working program written in C using the D2xx library calls. I'd like to replicate this functionality using pyftdi:

/**
 * Test CBUS bitbang interface on FT232 chip.
 *
 * Our goal is to wiggle CBUS bit 3, which in the FTDI USB-RS485 cable
 * controls the 5V drive circuitry on the output wires.
 *
 *   gcc -o bitbang bitbang.c -L. -lftd2xx -Wl,-rpath /usr/local/lib
 * cc bitbang.c -o bitbang -Wall -Wextra -lftd2xx -lpthread -lobjc -framework IOKit -framework CoreFoundation -Wl,-rpath /usr/local/lib -L/usr/local/lib
 */

#include "ftd2xx.h"
#include <WinTypes.h>
#include <stdio.h>
#include <unistd.h>

const UCHAR Drive03Hi=0x88;     /* CBUS03 configured as output, drive hi */
const UCHAR Drive03Lo=0x80;     /* CBUS03 configured as output, drive lo */

int main() {
  FT_HANDLE ftHandle;
  FT_STATUS ftStatus = FT_Open(0, &ftHandle);

  if(ftStatus != FT_OK) {
    fprintf(stderr, "FT_Open failed => %d\n", ftStatus);
    return 1;
  }
  // Repeatedly drive CBUS 03 high and then low
  while(ftStatus == FT_OK) {
    ftStatus = FT_SetBitMode(ftHandle, Drive03Hi, FT_BITMODE_CBUS_BITBANG);
    sleep(3);
    ftStatus = FT_SetBitMode(ftHandle, Drive03Lo, FT_BITMODE_CBUS_BITBANG);
    sleep(3);
  } 
  FT_Close(ftHandle);
}

[rdpoor]

Solved. But some documentation might help. Bitbang for CBUS is a bit strange, since the set_bitmode() mask argument defines the data direction and state of the bits -- there is no separate write function.

Working code example follows:

from pyftdi.ftdi import Ftdi
import time

ftdi = Ftdi()
ftdi.open_from_url('ftdi:///1')
while(True):
    ftdi.set_bitmode(0x88, Ftdi.BITMODE_CBUS)
    time.sleep(3)
    ftdi.set_bitmode(0x80, Ftdi.BITMODE_CBUS)
    time.sleep(3)
# never actually gets here...
ftdi.close()

[Zibri]

@rdpoor I get: AttributeError: type object 'Ftdi' has no attribute 'BITMODE_CBUS' :(

[eblot]

Please do not comment on tickets that are 4 years old, the code has evolved quite a bit since.

If there is an issue that is related to an existing ticket, open a new one and add a reference to it. Thanks.