What is TTL RGB signal in CNC displays?

TTL RGB (Transistor-Transistor Logic Red Green Blue) is a digital video signaling standard used in older CNC CRT displays. It uses 0-5V logic levels for each color channel plus separate horizontal and vertical sync signals. This differs from analog VGA where video signals are 0-0.7V analog.

Can I connect a TTL RGB CRT to a VGA monitor?

Not directly. TTL RGB operates at 5V logic levels while VGA uses 0.7V analog. Connecting TTL directly to VGA can damage the monitor. A TTL-to-VGA converter or a direct drop-in LCD replacement module is required. Kongto LCD modules accept TTL RGB directly.

What connector does FANUC use for CRT displays?

FANUC CRT displays use the Honda MR-20M 20-pin round connector. Pins 1-3 carry Red/Green/Blue video, pins 4-5 carry H/V sync, and pin 6 is chassis ground. Power is provided separately via DC 24V on pins 8-9 and 18-19.

What is the pinout for Siemens SINUMERIK CRT displays?

Siemens SINUMERIK CRT displays typically use a DB-25 (25-pin D-sub) connector. Pin 2 = Red, Pin 3 = Green, Pin 4 = Blue, Pin 6 = HSync, Pin 7 = VSync. Power varies by model — some use AC 110-220V, others DC 24V.

Do I need to rewire when replacing a CNC CRT with LCD?

With Kongto plug-and-play LCD modules, no rewiring is needed. Each module uses the exact same connector and pinout as the original CRT — Honda MR-20M for FANUC, 20-pin for Mitsubishi, DB-25 for Siemens. Just unplug the CRT and plug in the LCD.

CNC TTL RGB Signal Pinout Guide
FANUC, Mitsubishi, Siemens CRT to LCD Wiring Reference

Technical Reference Guide · Updated June 2026 · 10 min read

When replacing an aging CRT display on a CNC machine with a modern LCD module, understanding the TTL RGB signal pinout is critical. Each CNC manufacturer uses a different connector and signal arrangement. This guide provides the complete pin mapping for the three most common protocols: FANUC Honda MR-20M, Mitsubishi 20/26-pin, and Siemens DB-25.

            Key takeaway: Kongto plug-and-play LCD modules match the original pinout exactly — no rewiring, no adapter boards, no CNC parameter changes needed. This reference is provided for engineers who need to understand the signal path or are working with custom integrations.
        

1. What is TTL RGB?

TTL RGB is a digital video signaling standard. Unlike VGA which uses analog 0-0.7V signals, TTL RGB operates at 0-5V logic levels (TTL = Transistor-Transistor Logic). Key differences from VGA:

Parameter	TTL RGB (CNC CRT)	VGA (Standard Monitor)
Video Signal Level	0-5V Digital (On/Off per channel)	0-0.7V Analog (Continuous)
Number of Colors	8 (3-bit: 2³ R/G/B)	16.7M (8-bit per channel)
Sync Signal	Separate H & V (TTL 0-5V)	Separate or Composite H/V
Horizontal Freq	15.75 kHz (typically)	31-80 kHz
Connector	Varies by brand (see below)	DE-15 (HD-15)

⚠ Important: TTL RGB operates at 5V — connecting it directly to a standard VGA monitor input (which expects 0.7V) can damage the monitor's input circuits. Use a TTL-to-VGA converter or a dedicated CNC LCD replacement module.

2. FANUC — Honda MR-20M 20-Pin Connector

FANUC CRT displays (A61L series, MDT947B, D9MM-11A, D14CM-01A) use the Honda MR-20M 20-pin round connector. This is the most common interface in CNC CRT displays, found on FANUC 0, 0i, 16i, 18i, and 21i series controls.

Signal Pinout (viewed from display side)

Honda MR-20M (Female, Display Side) (1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) (14) (15) (16) (17) (18) (19) (20) Pin Signal Color Notes ───────────────────────────────── 1 Red Video Red 0-5V TTL 2 Green Video Green 0-5V TTL 3 Blue Video Blue 0-5V TTL 4 HSync Yellow Horizontal Sync (TTL) 5 VSync White Vertical Sync (TTL) 6 GND Black Chassis Ground 7 NC — Not Connected 8 DC +24V Red/White Power Supply (+) 9 DC +24V Red/White Power Supply (+) 10 GND Black Power Ground 11 GND Black Signal Ground (Red return) 12 GND Black Signal Ground (Green return) 13 GND Black Signal Ground (Blue return) 14 GND Black Signal Ground (HSync return) 15 GND Black Signal Ground (VSync return) 16-17 NC — Not Connected 18 DC +24V Red/White Power Supply (+) 19 DC +24V Red/White Power Supply (+) 20 GND Black Power Ground

Note: Some FANUC 9-inch monochrome CRTs use only the Green channel (Pin 2) for video — Red and Blue may be unused. The sync signals are always present on Pins 4 and 5.

Compatible Kongto LCD modules: A61L-0001-0093, A61L-0001-0074, A61L-0001-0092, D14CM-01A — all use direct Honda MR-20M connection.

3. Mitsubishi — 20-Pin / 26-Pin Connector

Mitsubishi CNC displays (MDT962B, BM09DF, MDT1283B, FCUA-CT100) typically use a 20-pin or 26-pin rectangular connector. The pinout varies slightly by model generation (M64 vs M500 vs M700).

Mitsubishi 20-pin Signal Pinout (MDT962B / BM09DF)

Pin	Signal	Notes
1	GND	Power/Signal Ground
2	GND	Power/Signal Ground
3	NC	Not Connected
4	Red Video	0-5V TTL
5	Green Video	0-5V TTL
6	Blue Video	0-5V TTL
7	NC	Not Connected
8	NC	Not Connected
9	HSync	Horizontal Sync (TTL)
10	VSync	Vertical Sync (TTL)
11	GND	Ground
12	GND	Ground
13	DC +24V	Power Supply
14	DC +24V	Power Supply
15	NC	Not Connected
16-20	GND	Ground

Compatible Kongto LCD modules: MDT962B LCD Upgrade

4. Siemens — DB-25 (25-Pin D-Sub) Connector

Siemens SINUMERIK CRT displays (6FC3998-7FA20, 6FC5103-0AB01, 6FC3997-7FA20) use a standard DB-25 female connector. The pinout follows the Siemens video interface standard.

Siemens DB-25 Signal Pinout

Pin	Signal	Notes
1	GND (Chassis)	Frame Ground
2	Red Video	0-5V TTL
3	Green Video	0-5V TTL
4	Blue Video	0-5V TTL
5	NC	Not Connected
6	HSync	Horizontal Sync (TTL)
7	VSync	Vertical Sync (TTL)
8	NC	Not Connected
9	NC	Not Connected
10	NC	Not Connected
11	GND	Ground
12	GND	Ground (Red return)
13	GND	Ground (Green return)
14-18	GND / NC	Various ground / not connected
19-25	GND	Ground

Note: Siemens CRT power varies by model. 6FC3998 series typically uses AC 110-220V internal supply, while 6FC5103 series uses DC 24V. Kongto LCD modules match the original power input of each specific model.

Compatible Kongto LCD modules: 6FC5103-0AB01, 6FC3988-7FA20

5. TTL to VGA Conversion

If you need to convert TTL RGB to standard VGA (e.g., for testing or using a standard monitor), the signal path requires:

Level shifting: TTL 5V signals must be attenuated to VGA 0.7V using resistor dividers or a dedicated converter IC
Sync adaptation: TTL sync (15.75 kHz) may need frequency doubling for modern VGA monitors that expect 31 kHz+
Connector conversion: Honda MR-20M or DB-25 to DE-15 (HD-15 VGA connector)

Kongto offers drop-in LCD replacement modules that bypass the need for conversion entirely — they accept TTL RGB directly and display at 800x600 or 1024x768 resolution. No level shifting or sync conversion needed.

6. Troubleshooting Common Signal Issues

Symptom	Probable Cause	Solution
No display (black screen)	Power supply failure, CRT dead, or signal cable disconnected	Verify DC 24V at connector pins. Check cable continuity. Replace CRT with LCD module.
Rolling image (no sync)	Missing or incorrect H/V sync signal	Check pins 4 (HSync) and 5 (VSync) continuity. Verify cable pinout matches display spec.
Wrong colors or missing color	One or more R/G/B channels disconnected	Check pins 1-3 (R/G/B) continuity. On monochrome CRTs, only Green channel is used.
Dim display	CRT tube aging, flyback transformer weak	Replace CRT with LCD module — brightness increases from ~200 to 400 cd/m².
Flickering / jitter	Power supply ripple, loose connections, CRT aging	Check DC 24V stability (should be ±5%). Replace CRT with flicker-free LCD.

7. Quick Reference: Pinout Comparison

Signal	FANUC (Honda MR-20M)	Mitsubishi (20-pin)	Siemens (DB-25)
Red Video	Pin 1	Pin 4	Pin 2
Green Video	Pin 2	Pin 5	Pin 3
Blue Video	Pin 3	Pin 6	Pin 4
HSync	Pin 4	Pin 9	Pin 6
VSync	Pin 5	Pin 10	Pin 7
Power (DC 24V)	Pins 8, 9, 18, 19	Pins 13, 14	Varies by model
Ground	Pins 6, 10-15, 20	Pins 1, 2, 11, 12, 16-20	Pins 1, 11-25

Frequently Asked Questions

Q: What is the voltage level of CNC TTL RGB signals?

A: Standard TTL levels are 0V (logic low) to +5V (logic high). This is consistent across FANUC, Mitsubishi, and Siemens CNC CRT interfaces. Some older systems may use +3.3V logic on newer revisions.

Q: Can I test my CNC CRT signals with a multimeter?

A: Yes. With the CNC powered on and running, measure DC voltage at the signal pins. H/V sync pins typically show 2-3V DC average (pulsing). Video pins show 0-5V depending on displayed content. A 5V DC reading on a video pin means that color channel is at full intensity.

Q: What if my CNC display has a different connector than listed here?

A: Some OEMs used custom connectors. Send a clear photo of your CRT display label and connector to [email protected] — our engineering team will identify the pinout and confirm compatibility within 24 hours.

CNC TTL RGB Signal Pinout GuideFANUC, Mitsubishi, Siemens CRT to LCD Wiring Reference