Industrial RGBHV Signal Analysis — From CGA/EGA to Modern Display
Keywords: RGBHV signal, CGA/EGA to VGA, industrial display technology, signal conversion
Target Audience: CNC engineers, industrial automation technicians, video signal system designers
1. Evolution of Industrial Video Signals
| Era | Signal Standard | Resolution | Refresh Rate | Typical Application |
|---|---|---|---|---|
| 1980s-1990s | CGA (Color Graphics Adapter) | 320x200 / 640x200 | 60 Hz | Early CNC controllers, industrial terminals |
| 1985-1995 | EGA (Enhanced Graphics Adapter) | 640x350 | 70 Hz | Upgraded CNC displays, PLC monitors |
| 1990-2005 | VGA (Video Graphics Array) | 640x480 / 800x600 | 60-85 Hz | FANUC CRT displays, industrial PCs |
| 2005-Present | SVGA/XGA Digital (DVI/HDMI) | 800x600 to 1920x1080 | 60-120 Hz | Modern LCD displays, HMI panels |
2. Understanding RGBHV Signal Architecture
2.1 What is RGBHV?
RGBHV stands for Red, Green, Blue, Horizontal Sync, Vertical Sync. It is a method of transmitting video signals using five separate channels:
- R, G, B: Three analog color channels, each carrying 0-0.7V peak-to-peak signals representing the primary colors
- H-Sync: Horizontal synchronization pulse that defines the start of each scan line
- V-Sync: Vertical synchronization pulse that defines the start of each frame
This separation provides superior signal quality compared to composite signals (CGA/EGA) because each color channel is isolated, preventing cross-talk and color bleeding.
2.2 Signal Timing Parameters
| Parameter | CGA | EGA | VGA | SVGA |
|---|---|---|---|---|
| Horizontal Frequency | 15.75 kHz | 21.85 kHz | 31.5 kHz | 37.9-48.9 kHz |
| Vertical Frequency | 60 Hz | 60 Hz | 60-85 Hz | 60-85 Hz |
| Pixel Clock | 14.3 MHz | 16.3 MHz | 25.2 MHz | 40-65 MHz |
| Color Depth | 4-bit (16 colors) | 6-bit (64 colors) | 8-bit (256 colors) | 24-bit (16.7M colors) |
| Signal Type | Digital TTL | Digital TTL | Analog 0.7Vpp | Analog 0.7Vpp |
3. CGA/EGA to RGBHV Conversion Process
3.1 Signal Type Conversion
The key challenge in converting CGA/EGA to RGBHV is the fundamental difference in signal types:
- CGA/EGA: Digital TTL signals (0V or 5V levels) — on/off for each color bit
- RGBHV/VGA: Analog signals (0-0.7V continuous) — proportional voltage for each color
A digital-to-analog converter (DAC) is required to translate TTL logic levels into proportional analog voltages. The Kongto Technology converter uses a high-speed video DAC with 8-bit resolution per channel, ensuring smooth color gradients.
3.2 Scan Rate Conversion
CGA operates at 15.75 kHz horizontal scan rate, while VGA requires 31.5 kHz. This means each CGA scan line must be doubled (line doubling) or the frame buffer must be scaled to match VGA timing. The converter handles this automatically using an integrated frame buffer and scaling engine.
3.3 Synchronization Signal Generation
CGA/EGA use composite sync (combined H+V on a single line), while RGBHV separates horizontal and vertical sync. The converter extracts and regenerates clean, separate H-Sync and V-Sync signals with proper timing.
4. Practical Conversion Solutions
| Input Signal | Output Signal | Converter Model | Key Features | Unit Price |
|---|---|---|---|---|
| CGA (15kHz) | RGBHV/VGA (31kHz) | JTX-CVR-001 | Auto-scan, plug-and-play, -20°C~+70°C | CNY 850 |
| EGA (22kHz) | RGBHV/VGA (31kHz) | JTX-CVR-002 | Auto-scan, plug-and-play, wide voltage 12-36V | CNY 880 |
| RGBS (composite sync) | RGBHV/VGA | JTX-CVR-003 | Sync separator, adjustable H/V position | CNY 750 |
| CGA+EGA (dual input) | RGBHV/VGA | JTX-CVR-004 | Auto-detect input type, dual-input switch | CNY 950 |
5. Signal Quality Verification
After conversion, verify the following signal quality metrics:
- Signal amplitude: R/G/B channels 0.7Vpp ±5% into 75Ω load
- Sync pulse width: H-Sync 3.8µs ±10%, V-Sync 64µs ±10%
- Rise/fall time: <5ns for clean edges
- Crosstalk: <-40dB between channels
- Impedance matching: 75Ω ±5% on all lines
For technical consultation on signal conversion solutions, contact Kongto Technology at szkongto01@foxmail.com