Display Controllers

The NanoVNA-H firmware supports three LCD display controllers. The appropriate driver is selected at compile time or auto-detected at boot.

Supported Controllers

Controller	Display Size	Resolution	Hardware
ILI9341	2.8 inch	320x240	NanoVNA-H
ST7789	2.8 inch	320x240	NanoVNA-H
ST7796S	4.0 inch	480x320	NanoVNA-H4

Controller Details

ILI9341

ILI9341 (ILITEK)

The ILI9341 is a 262K color TFT LCD controller commonly used in 2.8” displays.

Specifications:

Parameter	Value
Resolution	320 x 240 (QVGA)
Color Depth	16-bit (RGB565)
Interface	SPI (4-wire)
Read Pixel Size	3 bytes/pixel
Max SPI Clock	10 MHz (read), 50 MHz (write)

Firmware Configuration:

#define LCD_DRIVER_ILI9341
#define LCD_320x240

Touch Calibration Defaults:

#define DEFAULT_TOUCH_CONFIG {530, 795, 3460, 3350}

ST7789

ST7789 (Sitronix)

The ST7789 is a pin-compatible alternative to ILI9341 with similar characteristics.

Specifications:

Parameter	Value
Resolution	320 x 240
Color Depth	16-bit (RGB565)
Interface	SPI (4-wire)
Read Pixel Size	3 bytes/pixel
Compatibility	ILI9341 command set (partial)

Firmware Configuration:

#define LCD_DRIVER_ST7789
#define LCD_320x240

Auto-Detection:

The firmware can detect ILI9341 vs ST7789 at boot by reading the display ID register. Enable both drivers to allow auto-detection:

#define LCD_DRIVER_ILI9341
#define LCD_DRIVER_ST7789

ST7796S

ST7796S (Sitronix)

The ST7796S drives the larger 4.0” display on NanoVNA-H4.

Specifications:

Parameter	Value
Resolution	480 x 320 (HVGA)
Color Depth	16-bit (RGB565)
Interface	SPI (4-wire)
Read Pixel Size	2 bytes/pixel
Max SPI Clock	80 MHz

Firmware Configuration:

#define LCD_DRIVER_ST7796S
#define LCD_480x320

Touch Calibration Defaults:

#define DEFAULT_TOUCH_CONFIG {380, 665, 3600, 3450}

Display Memory Layout

Cell-Based Rendering

The firmware uses a cell-based dirty-region rendering system:

Parameter	320x240	480x320
Cell Width	32 pixels	32 pixels
Cell Height	32 pixels	32 pixels
Cells Wide	10	15
Cells High	8	10

Frame Buffer

The display does not use a full frame buffer. Instead:

1. A small SPI buffer holds cell data during rendering
2. Cells are rendered and transmitted one at a time
3. DMA can be used to overlap rendering and transmission

Buffer Size:

// Cell dimensions for 16-bit color
#define CELLWIDTH   (64/DISPLAY_CELL_BUFFER_COUNT)  // 32 pixels
#define CELLHEIGHT  32                               // 32 pixels
#define SPI_BUFFER_SIZE  (CELLWIDTH * CELLHEIGHT * DISPLAY_CELL_BUFFER_COUNT)

SPI Interface

Pin Connections

Signal	F072 Pin	F303 Pin	Description
SCLK	PB3	PB3	SPI clock
MOSI	PB5	PB5	Data to display
MISO	PB4	PB4	Data from display
CS	PB6	PB6	Chip select
DC	PB7	PB7	Data/Command
RESET	PA15	PA15	Hardware reset

DMA Mode

When __USE_DISPLAY_DMA__ is enabled:

• DMA1 Channel 5 handles SPI TX
• Double buffering allows parallel render/transmit
• Reduces CPU load during display updates

#define __USE_DISPLAY_DMA__
#define DISPLAY_CELL_BUFFER_COUNT  2  // Enable double buffering

Color Format

All controllers use RGB565 format with byte swapping for SPI:

// RGB565 format with byte swap for SPI
// Input: R(5), G(6), B(5) in standard order
// Output: gggBBBbb RRRrrGGG (byte-swapped for SPI)
#define RGB565(r,g,b)  ( (((g)&0x1c)<<11) | (((b)&0xf8)<<5) | ((r)&0xf8) | (((g)&0xe0)>>5) )

Display Palette

The firmware uses a 32-color palette for consistent colors:

Index	Name	Default Color	Usage
0	BG_COLOR	Black	Background
1	FG_COLOR	White	Foreground text
2	GRID_COLOR	Gray	Grid lines
3	MENU_COLOR	Light gray	Menu background
4	MENU_TEXT_COLOR	Black	Menu text
5	MENU_ACTIVE_COLOR	Gray	Selected menu item
6-9	TRACE_1-4_COLOR	Yellow, Cyan, Green, Magenta	Active traces
10-11	TRACE_5-6_COLOR	Red, Blue	Stored traces
12	NORMAL_BAT_COLOR	Green	Battery OK
13	LOW_BAT_COLOR	Red	Battery low
25	LINK_COLOR	Blue	Menu value text

Brightness Control

NanoVNA-H4 (F303)

The H4 supports adjustable backlight via DAC output:

#define __LCD_BRIGHTNESS__  // Enable brightness menu
#define DEFAULT_BRIGHTNESS  70  // 0-100%

Controlled via: CONFIG > BRIGHTNESS

NanoVNA-H (F072)

Standard NanoVNA-H does not support brightness control (fixed backlight).

Display Orientation

The display can be flipped 180 degrees:

Menu: CONFIG > EXPERT SETTINGS > FLIP DISPLAY

Shell command: config flip 1

This rotates both the display output and touch coordinates.

Touch Screen

The resistive touch panel uses ADC inputs:

Signal	F072 Pin	F303 Pin
XP	PA6	PA6
YP	PA7	PA7
XN	PB0	PB0
YN	PB1	PB1

Touch Calibration

Calibration stores 4 values: X min, X max, Y min, Y max

Menu: CONFIG > TOUCH CAL

Shell command: touchcal

Font Support

The firmware includes multiple font sizes:

Font ID	Size	File	Usage
0	5x7	Font5x7.c	Smallest
1	6x10	Font6x10.c	Default (320x240)
2	7x11	Font7x11b.c	Default (480x320)
3	11x14	Font11x14.c	Large
-	16x22	numfont16x22.c	Numeric keypad

Source Code Reference

Display driver code is located in:

• LCD driver: lcd.c
• Display defines: nanovna.h lines 509-618
• Color palette: nanovna.h lines 1193-1251
• Font data: fonts/*.c