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I am using a PiTFT 2.8" on an original Raspberry Pi B. I just reinstalled Raspbian and setup the PiTFT using the Adafruit easy install script to launch to console.

I have a python script that communicates using serial via USB on /dev/ttyUSB0. My script only runs correctly and accesses the USB port when an HDMI cable is plugged in. (If I unplug the HDMI, it won't communicate over serial; if I plug it in, it does.) I assume this has to do with a setting in /boot/config.txt, but I can't figure out which.

Here is config.txt:

# For more options and information see
# http://rpf.io/configtxt
# Some settings may impact device functionality. See link above for details

# uncomment if you get no picture on HDMI for a default "safe" mode
#hdmi_safe=1

# uncomment this if your display has a black border of unused pixels visible
# and your display can output without overscan
disable_overscan=0

# uncomment the following to adjust overscan. Use positive numbers if console
# goes off screen, and negative if there is too much border
#overscan_left=16
#overscan_right=16
#overscan_top=16
#overscan_bottom=16

# uncomment to force a console size. By default it will be display's size minus
# overscan.
#framebuffer_width=1280
#framebuffer_height=720

# uncomment if hdmi display is not detected and composite is being output
hdmi_force_hotplug=0

# uncomment to force a specific HDMI mode (this will force VGA)

# uncomment to force a HDMI mode rather than DVI. This can make audio work in
# DMT (computer monitor) modes
#hdmi_drive=2

# uncomment to increase signal to HDMI, if you have interference, blanking, or
# no display
#config_hdmi_boost=4

# uncomment for composite PAL
#sdtv_mode=2

#uncomment to overclock the arm. 700 MHz is the default.
#arm_freq=800

# Uncomment some or all of these to enable the optional hardware interfaces
#dtparam=i2c_arm=on
#dtparam=i2s=on
#dtparam=spi=on

# Uncomment this to enable the lirc-rpi module
#dtoverlay=lirc-rpi

# Additional overlays and parameters are documented /boot/overlays/README

# Enable audio (loads snd_bcm2835)
dtparam=audio=on

# --- added by adafruit-pitft-helper Wed May 15 16:54:04 CDT 2019 ---
dtparam=spi=on
dtparam=i2c1=on
dtparam=i2c_arm=on
dtoverlay=pitft28-resistive,rotate=270,speed=64000000,fps=30

Any help is much appreciated.

  • why are you assuming that the problem is with config.txt? .... your script is also suspect – jsotola May 16 at 3:05
  • The script only sends commands using pyserial. It works on headless Rasberry pi units and it works with this unit while HDMI is disconnected. – afikomen May 16 at 13:49
  • your post says the opposite, it communicates when the HDMI cable is connected – jsotola May 19 at 2:37
  • Yes. That was a typo. My apologies. The script only sends commands using pyserial. It works on headless Rasberry pi units and it doesn't work with this unit while HDMI is disconnected. – afikomen Jun 6 at 21:41

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