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Auxiliary Video Extension Pinout
Auxiliary Video Extension Signal Descriptions
Introduction
AVE Connector
Auxiliary Video Schematic
Related Registers
Introduction
Following text is extracted from "The Micro Channel Architecture
Handbook" Chet Heath and Winn L. Rosch, pages 125-127 Simon & Schuster
NY, NY. ISBN 0-13-583493-7 1990.
The video extension gives Micro Channel expansion boards
direct access to the various inputs of the digital-to-analog convertor
or DAC used by VGA. As it's name implies, the DAC makes analog signals
compatible with VGA monitors from the digital signals generated by the
computer's circuitry. By allowing access to the inputs of the DAC, the
Micro Channel video extension allows changes and improvements to be made
in the computer's video system without sacrificing monitor compatibility.
The video extension uses several important signals. Present here are
horizontal and vertical synchronizing signals plus a special control line
called ESYNC or enable sync line. This line determines whether the
synchronizing signals used in the video system original on the planar board or
from an adapter plugged into the Micro Channel. ESYNC is normally held to
logical high. Bringing it low enables the system to use the synchronizing
signals from the Micro Channel adapter.
Note: Video output can be passed in only one
direction at a time. The 'dot clock' signal cannot drive both EXTCLK to the VGA
and PCLK to the DAC.
Video data are transferred across the Micro Channel video extension in
digital form using eight video data lines. The data here are used to drive the
VGA Digital-to-Analog convertor on the system board.
Note: The full channel is available for use by the
adapter.
AVE Connector
The auxiliary video connector is a 20-pin connector located in-line with one
of the channel connectors on the system board.
Note: The 8580-Axx
planar and many older PS/55 planars have *two* AVE
slots. One for the "mandatory" Japanese Display
Adapter and the other for any other AVE adapter, like the
8514/A.
AVE Connector Pinout
See Auxiliary Video Extension Pinout.
AVE Signal Descriptions
See Auxiliary Video Extension Signal Descriptions.
Auxiliary Video Schematic
Source: PS/2
Hardware Interface Technical Reference May 1988 (Pages 487-490 physical)
Related Registers
Miscellaneous Output Register - Hex 03CC/03C2 (Page 432 physical)
Bits 3, 2: These two bits select the clock source. The external clock is
driven through the auxiliary video extension. The input clock should be kept
between 14.3 MHz and 28.4 MHz.
| Bits | Function |
|---|
| 3 | 2 |
|---|
| 0 | 0 | Selects 25.175 MHz clock for 640/320 Horizontal PELs |
| 0 | 1 | Selects 28.322 MHz clock for 720/360 Horizontal PELs |
| 1 | 0 | Selects External Clock |
| 1 | 1 | Reserved |
| 