VGA feature connector

VGA feature connector is a 8-bit expansion bus for VGA card standardized by VESA. That conenctor has been very popular for many years, but because it's limitations (not enough bandwidth for high resolutions and only 2560 color mode support) it is going to be replaces with something else. Some manufacturers (for example AT) have shifted to VESA Advanced Feature Connector.

From: [email protected] (Dominic H Goode)
Subject: VGA Feature Connector
Date: 12 Apr 93 22:59:42 GMT
Organization: Brunel University, Uxbridge, UK
X-Newsreader: TIN [version 1.1 PL8]
Does anyone know how the VGA video feature connector operates? I would like to know which of the pins are inputs, which are outputs, and which are bidirectional (if any - and how the direction is selected).I have found a pinout for the connector:

Video Feature Connector Pinouts

Pin     Name   Function
1       PD0    Dac Pixel data bit 0
2       PD1                   bit 1
3       PD2                   bit 2
4       PD3                       3
5       PD4                       4
6       PD5                       5
7       PD6                       6
8       PD7                       7
9       -      Dac Clock
10      -      Dac Blanking
11      -      Horizontal Sync
12      -      Vertical Sync
13      -      Ground

14      -      Ground
15      -      Ground
16      -      Ground
17      -      Select Internal Video
18      -      Select Internal Sync
19      -      Select Internal Dot Clock
20      -      Not Used
21      -      Ground
22      -      Ground
23      -      Ground
24      -      Ground
25      -      Not Used
26      -      Not Used
And I assume that pins 1 - 12 are outputs, and 17 - 19 are inputs. Is this correct?

The reason is this - I have a Rombo Media Pro+ video digitising card. It chroma keys its output into the vga monitor signal. However, although it is supposed to work with an ET-4000 with Hi-colour RAMDAC, the colours on screen behave as if the top 2 bits of colour information are missing, and red, green, blue signals are swapped around. Rombo has suggested that this may be due to insufficient buffering on the feature connector outputs, and is happy to sell me a buffer device for 50 pounds. I would rather save about 45 pounds, and build my own. I assume it would require (for example) a 74F244 buffer IC (or two).

Can anyone help? Any information on the feature connector would be highly appreciated!

Please could you reply by email : [email protected]

VGA feature connector

component side

pin     function
1       PD0 (DAC pixel data bit 0)
2       PD1 (DAC pixel data bit 1)
3       PD2 (DAC pixel data bit 2)
4       PD3 (DAC pixel data bit 3)
5       PD4 (DAC pixel data bit 4)
6       PD5 (DAC pixel data bit 5)
7       PD6 (DAC pixel data bit 6)
8       PD7 (DAC pixel data bit 7)
9       DAC clock
10      DAC blanking
11      Ext. horizontal sync
12      Ext. vertical sync
13      Ground

back side

pin     function
1       Ground
2       Ground
3       Ground
4       Select Internal Video
5       Select Internal Syncs
6       Select Internal DAC
8..11   Ground


ATI has used a connector called AMC in some of their cards. It seems that the AMC is just an "extended normal VGA feature connector", as far as the pinout is concerned.

ATI Technical Support feature connector info: The 26 pin BERG connector on ATI products is KEYED with pin Z13 missing and should be labelled as follows:

------------------------------------------------------------ -----

              Y1               J2                  Y13
             | .  .  .  .  .  .  .  .  .  .  .  .  . |
             | .  .  .  .  .  .  .  .  .  .  .  .    |
              Z1                                    Z13 (pin missing)
IBM defines the feature connector in the following manner:
Pin  Name  Description
Y1   C0   Colour BIT 0: an output when 'Select Internal Video' is hi.
Y2   C1   Colour BIT 1: an output when 'Select Internal Video' is hi.
Y3   C2   Colour BIT 2: an output when 'Select Internal Video' is hi.
Y4   C3   Colour BIT 3: an output when 'Select Internal Video' is hi.
Y5   C4   Colour BIT 4: an output when 'Select Internal Video' is hi.
Y6   C5   Colour BIT 5: an output when 'Select Internal Video' is hi.
Y7   C6   Colour BIT 6: an output when 'Select Internal Video' is hi.
Y8   C7   Colour BIT 7: an output when 'Select Internal Video' is hi.

Y9        DAC Clock     Video clock for adapter palette/DAC.  Output when
'Select Internal DAC Clock' is high.

Y10  DAC Blanking   Blanking Signal for adapter palette/DAC. Output when 'Select
Internal Syncs' is high.

Y11  Ext. H Sync    Output when 'Select Internal Syncs' is high.

Y12  Ext. V Sync    Output when 'Select Internal Syncs' is high.

Y13, Z1, Z2, Z3, Z8, Z9, Z10 & Z11 Ground

Z4   Select Internal Defines colour pins (C7 to C0) as outputs when high.
(Video) The adapter pulls this signal to +5 volts through a 4.7K ohm resistor.

Z5   Defines SYNCS and blanking pins as outputs.  The adapter uses 4.7K ohm
pull-up resistor.

Z6   Defines the DAC Clock pin as an output.

Z7, Z12 & Z13          Not used
ATI card connector pinouts are from Tan Irwin at ATI Technical Support.