Auxiliary Video Extension (AVE)

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.

BitsFunction
32
00Selects 25.175 MHz clock for 640/320 Horizontal PELs
01Selects 28.322 MHz clock for 720/360 Horizontal PELs
10Selects External Clock
11Reserved

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