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.
| Pin | Signal | 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 | 1V SOUND | 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. |