VGA & Serial interface for Raspberry Pi 400
Like VGA666, this pcb uses dpi interface (in mode 7, and 3x4bits to free gpio 12 to 15)
see https://www.raspberrypi.org/documentation/hardware/raspberrypi/dpi/README.md
only the necessary bits of the dpi are redirected to the 40-pin GPIO port, with the 'gpio=2-3,8-11,16-19,24-27=a2' line on config.txt
/boot/config.txt
# replace dtoverlay=vc4-kms-v3d with
dtoverlay=vc4-fkms-v3d
# disable i2c, pin use by h-sync & v-sync
dtparam=i2c_arm=off
gpio=2-3,8-11,16-19,24-27=a2
dpi_output_format=0x17
enable_dpi_lcd=1
display_default_lcd=1
dpi_group=2
dpi_mode=16
#---------------- dpi_mode line ---------------------
#---> 640x480 60hz dpi_mode=4
#---> 800x600 60hz dpi_mode=9
#---> 1024x768 60hz dpi_mode=16
#---> 1280x768 60hz dpi_mode=23
#---> 1280x800 60hz dpi_mode=28
#---> 1280x960 60hz dpi_mode=32
#---> 1280x1024 60hz dpi_mode=35
#---> 1360x768 60hz dpi_mode=39
#---> 1366x768 60hz dpi_mode=81
#---> 1400x1050 60hz dpi_mode=42
#---> 1440x900 60hz dpi_mode=47
#---> 1600x1200 60hz dpi_mode=51
#---> 1680x1050 60hz dpi_mode=58
#---> 1920x1080 60hz dpi_mode=82
#---> 1920x1200 60hz dpi_mode=69
#---> 1920x1440 60hz dpi_mode=73
# Enable Uart /dev/ttyAMA1, on pin 12,13,14,15
dtoverlay=uart5,ctsrts
copy content of config-example.txt to /boot/config.txt
install Minicom
sudo apt update
sudo apt upgrade
sudo apt install minicom
run minicom with default config
minicom -D /dev/ttyAMA1
run minicom 9600bps 8bit
minicom -b 9600 -8 -D /dev/ttyAMA1
rev1 bad space between VGA and DB9 connectors
rev2