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Apple II Video Expansion


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.

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.

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.

Contributor: Joakim Ögren

Apple Tech Info Library 1419: Apple IIc, External Pinouts at Apple TIL homepage

Copyright © The Hardware Book Team 1996-2001.
May be copied and redistributed, partially or in whole, as appropriate.
Document last modified: 2000-07-08