Apple IIc Video Port Breakout

During KansasFest 2020 there was a talk about video output options for the Apple IIc. A Apple IIc adapter Audio/Video out connector being sold on eBay was demonstrated. Like everybody else in attendance, I purchased one of these Audio/Video breakout adapters.



The adapter is well put together. It is true that there is a built-in NTSC video port on the Apple IIc. However, the Monitor port includes audio support and a higher quality video output than the built-in video port.


As we learned during the KansasFest presentation, it turns out that the Apple IIc video port includes and audio and video breakout.



1TEXTVideo text signal from TMG; set to inverse of GR, except in double high-resolution mode.
214M14M master timing signal from the system oscillator.
3SYNC*Displays horizontal and vertical synchronization signal from IOU pin 39.
4SEGBDisplays vertical counter bit from IOU pin 4; in text mode, indicates second low-order vertical counter; in graphics mode, indicates low-resolution.
51V SOUNDOne-volt sound signal from pin 5 of the audio hybrid circuit (AUD).
6LDPS*Video shift-register load enable from pin 12 of TMG.
7WNDW*Active area display blanking; includes both horizontal and vertical blanking.
8+12VRegulated +12 volts DC; can drive 300mA.
9PRAS*RAM row-address strobe from TMG pin 19.
10GRGraphics mode enable from IOU pin 2.
11SEROUT*Serialized character generator output from pin 1 of the 74LS166 shift register.
12NTSCComposite NTSC video signal from VID hybrid chip.
13GNDGround reference and supply.
14VIDD7From 74LS374 video latch; causes half-dot shift high.
15CREFColor reference signal from TMG pin 3; 3.58 MHz.
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