DB-25

DB-25 is a 25-pin D-subminiature connector, the largest of the common D-sub sizes used on consumer and professional electronics. In the CRT world it is best known as the "multi connector" or "computer input" found on Japanese professional monitors of the 1980s, where a single 25-pin socket carried analog RGB, digital TTL RGB, sync, blanking, audio and mode-select lines.

Unlike DE-15 (VGA), which standardised on a single analog signalling scheme, DB-25 video connectors were manufacturer-specific: the pinout of a Sony CMPTR input has nothing in common with, say, an Apple or Atari 25-pin port. The pin assignment must always be taken from the individual machine's manual.

Use on Sony professional monitors

Sony fitted a 25-pin CMPTR (computer) connector to several early Trinitron professional monitors, including the PVM-2030 and PVM-2530. The connector accepts both analog and digital RGB, selected by pulling mode pins high or low:

Pin	Signal	Notes
1	IBM select	High (5 V) selects IBM mode; low selects 3-bit TTL
2	Audio select	High takes audio from pin 13; low takes audio from the LINE A/B or VTR inputs
3	H sync or composite sync	1 Vp-p 75 Ω in analog mode, TTL in digital mode; negative polarity
4	Blue input	0.7 Vp-p analog / TTL digital
5	Green input	1 Vp-p when sync-on-green is used
6	Red input	0.7 Vp-p analog / TTL digital
7–8	No connection
9	Analog/digital mode select	Open = analog (0.7 Vp-p); grounded = digital (TTL)
10	RGB/NORMAL mode select	High = RGB from computer; low = composite from LINE A/B or VTR
11	V sync	TTL, negative polarity
12	Blanking	Low superimposes the composite input over the computer picture
13	Audio input	−5 dB, input impedance greater than 47 kΩ
14	No connection
15–24	Ground
25	IBM luminance signal	TTL, active when pin 1 is high

Because pins 3 and 11 carry horizontal and vertical sync separately, and pin 3 alternatively accepts composite sync, the same socket supports RGBHV, RGBS, RGsB and TTL RGB sources.

Other uses

The DB-25 was also the original IBM PC serial port connector (later replaced by the DB-9), the standard IBM PC parallel/printer port connector, and the SCSI-1 connector on Apple Macintosh computers. None of these are video applications, but the physical connector is identical, so a 25-pin cable found with vintage equipment cannot be identified by its shell alone.

See also

• DB-9 — 9-pin D-sub used for CGA/EGA TTL RGB
• DE-15 (VGA) — 15-pin D-sub used for analog VGA
• EIAJ-8 — 8-pin rectangular connector used for TTL RGB on Japanese equipment