The MicroFTX is a low-cost, reconfigurable, and compact Micro-USB breakout board based on the FTDI FT230X full-speed USB Serial UART IC.

Uses

• USB to serial interface for microcontroller development or debugging
  
• Reverse-engineering tool with flexible I/O voltages (1.8V, 2.5V, 3.3V, etc)
• Battery charger detection for high-power USB applications (app note)
• Bitbang GPIO mode for simple digital input and output

Features

• FT230XQ (website, datasheet) from FTDI’s new X-Chip series
• Revision D silicon (date code 1246-D)
• Tiny footprint – only 0.4" x 0.64" including Micro-USB B connector
• Standard 0.1" headers expose all signals
• Easy solder-jumper configuration
• Supports I/O voltages from 1.8V to 3.3V, with 5V tolerance
• UART baudrates up to 3 Mbaud
• Solid FTDI driver support for Windows, OS X, and Linux
• Programming interface is similar to the FT232R series chips
• Internal reprogrammable EEPROM for VID/PID and other customization
• Professionally manufactured, with gold plating for easy solderability
• Unique pre-programmed serial number
• Open design
• Low cost, and bulk discounts are available, at the jim.sh store

Pinout

10 signals are brought out to pin holes with 0.1" spacing. They fit standard 0.1" male or female headers, or it’s also easy to just solder wires directly.

For many uses, the four pins along the lower edge (V, RX, TX, GND) are all you’ll need. The signal names are shown on the bottom of the PCB.

Most of these pins are configurable! The CBx pins have a bunch of options that can be changed by reprogramming the EEPROM. Even without changing the EEPROM, it’s easy to reuse the CTS, RTS, RX, and TX pins as simple digital I/O.

Looking at the bottom of the PCB, counterclockwise from the top left:

Jumper Configuration

The MicroFTX has four solder jumpers on the bottom side, labeled J1 through J4, that configure how voltages are connected between the FTDI chip, the V pin, and the USB port.

You can choose a solder jumper configuration when purchasing the MicroFTX, but it’s also easy to change at any time.

To close a solder jumper, add solder to both pads until a bridge is formed between them.
To open a previously-closed solder jumper, use a clean soldering iron or wick to remove the excess solder until the bridge goes away.

Valid configurations

	J1	J2	J3	J4	Power Source	V pin	I/O voltage	Notes
#1					USB	5V out	3.3V	a, b
#2					USB	3.3V out	3.3V	a, c
#3					USB	1.8V - 3.3V in	1.8V - 3.3V	d
#4					V pin	5V in	3.3V	a
#5					V pin	3.3V in	3.3V	a
#6					USB	no connection	3.3V	a
Notes: I/O voltage is 5V tolerant 5V output current is limited by what the USB port can supply 3.3V output current is 50mA max I/O voltage is set by the voltage applied to the V pin

Other jumper configurations will result in the board not powering up, or could potentially damage the chip.

Drivers

sudo add-apt-repository ppa:canonical-kernel-team/ppa
sudo apt-get update
sudo apt-get install linux-headers-generic-pae linux-image-generic-pae

$ adduser $USER dialout

SUBSYSTEM=="usb", ACTION=="add", \
  ATTRS{idVendor}=="0403", ATTRS{idProduct}=="6015", GROUP="plugdev"

Comparison to Older Chips

The FT230X is very similar to FTDI’s older chips, like the FT232R series. In general, a lot of code and tools for the FT232R are likely to work with few changes.

Bitbang GPIO

The FT230X supports bitbang GPIO (general-purpose input/output) modes that allow you to set and read digital pins directly. It’s a great way to let your computer drive a simple binary output, or to read the state of a switch. For full details, see the FT230X website and datasheet. FTDI’s bitbang app note AN232R-01 hasn’t been updated for the FT-X series of chips yet, but the setup and usage of bitbang mode is essentially the same.

Two forms of bitbang are supported. They are enabled with FD_SetBitMode (D2XX) or ftdi_set_bitmode (libftdi):

• BITMODE_BITBANG uses the RX, TX, CTS, and RTS pins and works out of the box
• BITMODE_CBUS uses the CBx pins, but needs to be enabled first in the EEPROM

On Linux, libftdi provides a pretty easy way to use bitbang. The python bindings are poor, but it’s straightforward in C. This program will toggle the RX, TX, CTS, and RTS pins every time it’s run:

#include <ftdi.h>
#include <err.h>

int main(int argc, char *argv[])
{
    struct ftdi_context ftdi;
    unsigned char x;

    /* Initialize and find device */
    if (ftdi_init(&ftdi) < 0)
        err(1, "ftdi_init");

    if (ftdi_usb_open(&ftdi, 0x0403, 0x6015) < 0)
        err(2, "can't open device");

    /* Enable bitbang */
    if (ftdi_set_bitmode(&ftdi, 0xff, BITMODE_BITBANG) < 0)
        err(3, "can't enable bitbang mode");

    /* Read state & flip it */
    if (ftdi_read_pins(&ftdi, &x) < 0)
        err(4, "can't read");
    x ^= 0xff;
    if (ftdi_write_data(&ftdi, &x, 1) < 0)
        err(5, "can't write");

    /* Close device */
    ftdi_usb_close(&ftdi);
    ftdi_deinit(&ftdi);

    return 0;
}

To test it out, download this file as ftdi-bitbang.c, compile, and run it:

$ sudo apt-get install libftdi-dev build-essential
$ gcc -o ftdi-bitbang ftdi-bitbang.c -lftdi
$ ./ftdi-bitbang

Non-standard Baudrates

The FT230X supports custom baudrates up to 3Mbaud. If you’re using Python’s pySerial module, custom baudrates should just work like any other baudrate:

#!/usr/bin/python
import serial

ser = serial.Serial(port = "/dev/ttyUSB0", baudrate = 2000000)
ser.write("hello, world")
ser.close()

Here is a low-level example of how to configure custom baudrates in C on a Linux system:

#include <termio.h>
#include <fcntl.h>
#include <err.h>
#include <linux/serial.h>

static int rate_to_constant(int baudrate) {
#define B(x) case x: return B##x
    switch(baudrate) {
        B(50);     B(75);     B(110);    B(134);    B(150);
        B(200);    B(300);    B(600);    B(1200);   B(1800);
        B(2400);   B(4800);   B(9600);   B(19200);  B(38400);
        B(57600);  B(115200); B(230400); B(460800); B(500000); 
        B(576000); B(921600); B(1000000);B(1152000);B(1500000); 
    default: return 0;
    }
#undef B
}    

/* Open serial port in raw mode, with custom baudrate if necessary */
int serial_open(const char *device, int rate)
{
    struct termios options;
    struct serial_struct serinfo;
    int fd;
    int speed = 0;

    /* Open and configure serial port */
    if ((fd = open(device,O_RDWR|O_NOCTTY)) == -1)
        return -1;

    speed = rate_to_constant(rate);

    if (speed == 0) {
        /* Custom divisor */
        serinfo.reserved_char[0] = 0;
        if (ioctl(fd, TIOCGSERIAL, &serinfo) < 0)
            return -1;
        serinfo.flags &= ~ASYNC_SPD_MASK;
        serinfo.flags |= ASYNC_SPD_CUST;
        serinfo.custom_divisor = (serinfo.baud_base + (rate / 2)) / rate;
        if (serinfo.custom_divisor < 1) 
            serinfo.custom_divisor = 1;
        if (ioctl(fd, TIOCSSERIAL, &serinfo) < 0)
            return -1;
        if (ioctl(fd, TIOCGSERIAL, &serinfo) < 0)
            return -1;
        if (serinfo.custom_divisor * rate != serinfo.baud_base) {
            warnx("actual baudrate is %d / %d = %f",
                  serinfo.baud_base, serinfo.custom_divisor,
                  (float)serinfo.baud_base / serinfo.custom_divisor);
        }
    }

    fcntl(fd, F_SETFL, 0);
    tcgetattr(fd, &options);
    cfsetispeed(&options, speed ?: B38400);
    cfsetospeed(&options, speed ?: B38400);
    cfmakeraw(&options);
    options.c_cflag |= (CLOCAL | CREAD);
    options.c_cflag &= ~CRTSCTS;
    if (tcsetattr(fd, TCSANOW, &options) != 0)
        return -1;

    return fd;
}

Download this example: linux-custom-baudrate.c.

EEPROM Customization

The FT230X includes a 2048-byte reprogrammable EEPROM that configures the chip. Features that can be customized in the EEPROM include:

• USB vendor ID, product ID, device strings
• Device serial number
• I/O pin drive strength
• UART signal polarity inversion
• CBUS pin configuration, allowing each pin to be selected as:
  • TX/RX LED outputs
  • Clock output (6 MHz, 12 MHz, 24 MHz)
  • USB frame toggle (toggles every USB frame)
  • USB sleep status and control
  • Battery charge detection output
  • Bitbang GPIO
  • etc.

The easiest way to reprogram the EEPROM is using FTDI’s FT_Prog utility for Windows. Version 2.6.6 and later support the FT-X series chips. The user manual has more information.

The open-source libftdi library includes functions to access and change the EEPROM contents, and a standalone utility ftdi_eeprom that uses these functions. However, libftdi’s FT-X support is not necessarily complete and may not yet have been updated to support the FT-X chips. Note that incorrectly changing the EEPROM contents may lead to a chip that is difficult to recover.

Design Files

Use these for reference, or if you want to incorporate this design into your own boards. Note that Eagle 6 is required to open the layout files.

• ftx-schematic.pdf (PDF schematic)
• ftx-layout.pdf (PDF layout)
• ftx.zip (Eagle PCB schematic and layout)

FTDI Errata

FTDI has announced some errors in early (Revision B) versions of the FT230XQ chip, which were used in MicroFTX boards sold in 2012. These errors, and their workarounds, are detailed in FTDI’s Technical Note TN_139.

Current MicroFTX boards are shipping with Revision D or later silicon, which resolves all known issues.

Purchasing and Contact

The MicroFTX is available at the jim.sh store.

For questions or comments, e-mail support@jim.sh.