Apple II Video Expansion

15 PIN UNKNOWN CONNECTOR

Pin	Name	Description
1	TEXT	Video text signal from TMG; set to inverse of GR, except in double high-resolution mode.
2	14M	14M master timing signal from the system oscillator.
3	SYNC*	Displays horizontal and vertical synchronization signal from IOU pin 39.
4	SEGB	Displays vertical counter bit from IOU pin 4; in text mode, indicates second low-order vertical counter; in graphics mode, indicates low-resolution.
5	1VSOUND	One-volt sound signal from pin 5 of the audio hybrid circuit (AUD).
6	LDPS*	Video shift-register load enable from pin 12 of TMG.
7	WNDW*	Active area display blanking; includes both horizontal and vertical blanking.
8	+12V	Regulated +12 volts DC; can drive 300mA.
9	PRAS*	RAM row-address strobe from TMG pin 19.
10	GR	Graphics mode enable from IOU pin 2.
11	SEROUT*	Serialized character generator output from pin 1 of the 74LS166 shift register.
12	NTSC	Composite NTSC video signal from VID hybrid chip.
13	GND	Ground reference and supply.
14	VIDD7	From 74LS374 video latch; causes half-dot shift high.
15	CREF	Color reference signal from TMG pin 3; 3.58 MHz.

Note:
The signals at the DB-15 on the Apple IIc are not the same as those at the DB-15 end of the Apple III, Apple IIGS, and Macintosh II. Do not attempt to plug a cable intended for one into the other.

Note:
Several of these signals, such as the 14 MHz, must be buffered within about 4 inches of the back panel connector--preferably inside a container directly connected to the back panel.

Source: [The Hardware Book]

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