Video Signal Conversion Systems — CGA/EGA to VGA, RGB to VGA Guide
Keywords: CGA to VGA converter, EGA to VGA converter, RGB to VGA, video signal conversion system
1. Overview of Signal Conversion Scenarios
Industrial video signal conversion is essential when upgrading legacy CNC displays to modern LCD monitors. This guide covers the three most common conversion scenarios:
| Conversion Type | Input Signal | Output Signal | Primary Challenge |
|---|---|---|---|
| CGA to VGA | Digital TTL 15kHz | Analog RGBHV 31kHz | Digital-to-analog + scan rate doubling |
| EGA to VGA | Digital TTL 22kHz | Analog RGBHV 31kHz | Digital-to-analog + scan rate conversion |
| RGB to VGA | Analog RGBS/RGBHV | Analog RGBHV (standard VGA timing) | Sync separation + timing normalization |
2. CGA to VGA Conversion
2.1 Technical Details
CGA (Color Graphics Adapter) was introduced by IBM in 1981 and outputs 4-bit digital TTL signals at 15.75kHz horizontal frequency. To display CGA output on a modern VGA monitor:
- DAC conversion: Translate 4-bit TTL digital signals (0V/5V) to analog RGB signals (0-0.7V)
- Line doubling: Double the horizontal scan rate from 15.75kHz to 31.5kHz (VGA standard)
- Frame buffer scaling: Scale 320x200 or 640x200 resolution to 640x480 or 800x600
- Sync generation: Generate standard VGA H-Sync and V-Sync signals
2.2 Implementation
Kongto Technology JTX-CVR-001 converter handles all four steps automatically. Installation requires only connecting the CGA output cable to the converter input and the VGA output to the LCD display.
3. EGA to VGA Conversion
3.1 Technical Details
EGA (Enhanced Graphics Adapter) outputs 6-bit digital TTL signals at 21.85kHz. EGA conversion is similar to CGA but with:
- 6-bit color depth (64 colors vs. CGA's 16 colors)
- Higher horizontal frequency (21.85kHz vs. 15.75kHz)
- 640x350 native resolution
4. RGB to VGA Conversion
4.1 RGBS vs RGBHV
Many FANUC systems output analog RGB signals with composite sync (RGBS) rather than separate H/V sync (RGBHV). VGA monitors require separate sync signals. The conversion process:
- Sync separation: Extract horizontal and vertical sync pulses from the composite sync signal using a dedicated sync separator IC
- Signal conditioning: Clean up sync edges and adjust pulse widths to VGA specifications
- Impedance matching: Ensure 75Ω source impedance on all output lines
5. Comparison of Conversion Solutions
| Parameter | JTX-CVR-001 (CGA) | JTX-CVR-002 (EGA) | JTX-CVR-003 (RGB) |
|---|---|---|---|
| Input Signal | CGA TTL 15kHz | EGA TTL 22kHz | RGBS analog |
| Output Signal | VGA 640x480@60Hz | VGA 640x480/800x600@60Hz | VGA 640x480/800x600@60Hz |
| Color Depth | 8-bit per channel | 8-bit per channel | 8-bit per channel |
| Operating Temp | -20°C to +70°C | -20°C to +70°C | -20°C to +70°C |
| Power | 12-36 VDC | 12-36 VDC | 12-36 VDC |
| MTBF | 50,000 hours | 50,000 hours | 50,000 hours |
| Price | CNY 850 | CNY 880 | CNY 750 |
Contact Kongto Technology at szkongto01@foxmail.com for product inquiries.