ArtyZ7-20-NHD-2.4-TFT

FPGA VHDL project for the ArtyZ7-20 board driving the NHD-2.4-240320CF TFT display (ST7789S driver IC, inteface 16 bit parallel).

This is a driver for a Newhaven 2.4" TFT display (http://www.newhavendisplay.com/tfts-24-tfts-c-1_590.html). It reads the HDMI IN video signals, extracts a 320x240 pixel area and sends this to the TFT display via the 16 bit parallel interface.

A 320x240 area of the Raspberry Pi's desktop rendered on the TFT

The whole 640x480 desktop (crudely) downscaled to the 320x240 TFT pixels

The driver init code sets up the 16-bit parallel interface to the color mode 65K RGB with 5/6/5 bits for the red/green/blue pixel values.

A write cycle for transferring a single 16 bit display pixel takes a minimum time of 66 ns according to the ST7789S data sheet, page 40. To be on the safe side, the driver implements a write cycle period of 80 ns. Even with the 80 ns we can achieve a refresh rate of 320x240 pixels x 80 ns = 6.144 milliseconds per frame, which is roughly 160 frames per second.

The VHDL project was developed and tested on the Diligent ArtyZ7-20 board, but should run on any FPGA board with a HDMI IN or DVI IN connector that is supported by the Vivado IDE.

Software and IP versions

The project was created using the free Vivado Webpack Editor 2018.1 and the included Vivado IP:

• clk_wiz / Clocking Wizard v6.0
• blk_mem_gen / Block Memory Generator v8.4 (Rev. 1)

plus the free Diligent IP for Vivado from Github:

• dvi2rgb / DVI to RGB Video Decoder (Sink) v1.9 (Rev. 1)
• rgb2dvi / RGB to DVI Video Encoder (Source) v1.4 (Rev. 7)
• ila / Integrated Logic Analyzer v6.2 (Rev. 6)

Physical setup

Part list:

• Diligent Arty Z7-20 FPGA development board
• NHD-2.4-240320CF-CSXN-F TFT display with ST7789S driver IC
• NHD-FFC40 Breakout-Board (40 pin, 0.5mm pitch)

Connecting the NHD TFT to the Arty

• Power supplied via USB or REG to the Arty board
• HDMI IN connected to video source, max 1920x1080 @ 60 Hz (I used a Raspberry Pi for testing, resolution set to 640x480)
• HDMI OUT (optional) connected to external monitor, the video data from HDMI IN is passed through to HDMI OUT
• Connect the TFT Pins from the FFC40 breakout to the Arty's IO (I used simple jumper wires) like this:

          TFT   ARTY  
    ---------   ---------   
       GND  1   GND  
        NC  2   -  
        NC  3   -    
        NC  4   -  
        NC  5   -   
        NC  6   -  
       VDD  7   3V3   
     IOVDD  8   3V3 (typical 1.8V, max 3.3V)   
        NC  9   -   
       /CS 10   GND (= CS is always enabled)   
       D/C 11   IO9   
       /WR 12   IO10   
       /RD 13   3V3 (the read function is not used)   
       DB0 14   IO0   
       DB1 15   IO1   
       DB2 16   IO2   
       DB3 17   IO3   
       DB4 18   IO4   
       DB5 19   IO5   
       DB6 20   IO6   
       DB7 21   IO7   
       DB8 22   IO26   
       DB9 23   IO27   
      DB10 24   IO28   
      DB11 25   IO29   
      DB12 26   IO30   
      DB13 27   IO31   
      DB14 28   IO32   
      DB15 29   IO33   
      /RES 30   IO8   
       IM0 31   GND (= selects the 16 bit interface)   
        NC 32   -   
       GND 33   GND   
    LED-K1 34   GND   
    LED-K2 35   GND   
    LED-K3 36   GND   
    LED-K4 37   GND   
     LED-A 38   3V3   
       GND 39   GND   
        NC 40   -    

Creating the Vivado project

1. Download and install the Vivado Webpack Edition
   https://xilinx.com/support/download.html

2. Download and install the Arty Z7-20 board files
   https://github.com/Digilent/vivado-boards

3. Download and unzip the Digilent Vivado IP library release "vivado-library-2016.4.zip"
   https://github.com/Digilent/vivado-library/releases
   To add the unzipped Diligent IP folder to the Vivado Editor's "IP Defaults" settings, go to the "Tools" menu in Vivado, choose "Settings" and then "IP Defaults" in the left column. Then press the "+" button and select the folder you unzipped the Diligent IP to, in my case "C:\Diligent_Vivado_IP".

4. Download the files from the "source" folder of this repository onto your harddrive.
   I recommend using a short path name that does not contain spaces, in my case "C:\NHD"

   C:\NHD\ArtyZ7_20Master.xdc
   C:\NHD\create_project.tcl
   C:\NHD\Driver_16bitParallel.vhd
   C:\NHD\Main_wrapper.vhd
   C:\NHD\Main.bd
   C:\NHD\NHD_24_240320CF_Init.vhd
   C:\NHD\NHD_24_240320CF.vhd
   C:\NHD\VideoProcessing.vhd

5. Create the project by running the included create_project.tcl script

• Open the create_project.tcl script with a text editor, locate line 158:
  set_property "ip_repo_paths" "[file normalize "C:/Diligent_Vivado_IP"]" $obj
  change C:/Diligent_Vivado_IP to the path where you unzipped your IP to in step (3), using forward slashes in the path name

• Start the Vivado 2018.1 Editor
  On the welcome page, you can see the tcl console at the bottom

• Type "cd C:/NHD" (adjust the path to where you put your source files on your harddisk in step (4) - again, using forward slashes instead of backslashes) into the tcl console prompt, then press return

• Type "source ./create_project.tcl" into the tcl console prompt and press return

The Vivado project "ArtyZ7-20-NHD" is generated and opened in the Vivado Editor.

The block design diagram of the ArtyZ7-20-NHD project

Runtime options

The two switches SW0 and SW1 on the Arty board can be used to configure the display content:

SW0 changes the resolution on the tft
when switched on, only every other pixel is written to the block ram, so an area of 640x320 pixels is (crudely) downscaled to th 240x320 tft size

SW1 can be used for testing the driver functionality without an HDMI signal
when switched off, a full screen red-green-blue sequence is shown on the tft

Offsetting the TFT display area

The 320x240 pixel area that is output to the TFT has its origin by default at the upper left corner (0/0) of the HDMI frame. If you want to move the area to some other location within the HDMI frame, you can change the values of the constants h_start and v_start in the VideoProcessing.vhd file at line numbers 42 and 46 respectively.