Editing Enhanced Graphics Adapter (section)

=== Specifications ===
[[File:Numbered DE9 female Diagram.svg|thumb|right|EGA connector pinout when looking at back of computer]]
EGA uses a female nine-pin D-subminiature ([[DE-9]]) connector for output, identical to the CGA connector. The signal standard and pinout is backward-compatible with CGA, allowing EGA monitors to be used on CGA cards and conversely.

When operating in EGA modes, pins 2, 6 and 7 are repurposed for EGA's secondary RGB signals (see pinout table below). When operating in 200-line CGA modes, the EGA card is fully backward compatible with a standard IBM CGA monitor; however, third-party monitors had varying compatibility.{{Citation needed|date=August 2020}}

[[File:Tvm-md-3-prevga-monitor-front-and-rear.jpg|thumb|right|Front and rear views of the TVM MD-3, a third-party EGA monitor. DE-9 input, mode switch, contrast and brightness controls at front, V&nbsp;size and V&nbsp;hold knobs at rear.]]

Third-party monitors sometimes connected pin two to ground internally. When connected to an EGA card, this shorts the EGA's secondary red output to ground and can damage the card. Also, some monitors were wired with pin two as their sole ground, and these will not work with the EGA.{{Citation needed|date=August 2020}}

Conversely, an EGA monitor should work with a CGA adapter, but if it is not set to CGA mode, the secondary red signal will be grounded (always zero), and the secondary blue will be floating (unconnected), causing all high-intensity colors except brown to display incorrectly, and all colors to potentially have a variable blue tint due to the indeterminate state of the unconnected secondary blue.{{Citation needed|date=August 2020}}

The IBM 5154 EGA monitor has a special IBM 5153 CGA compatibility mode when operating with CGA sync signals and automatically changes to the CGA pinout to avoid all of the mentioned problems when operating in this mode.<ref>IBM Options and Adapters, Volume 1, "Enhanced Color Display", page 4: "When operating in Mode 1, the display maps the 4 input bits into 16 of the possible 64 colors as shown in the following chart." August 2, 1984.</ref>
{| class="wikitable"
|+ EGA DE-9 connector pin signals
|-
! Pin
! Name
! EGA modes
! CGA compatible modes
|-
| 1
| GND
| Ground
| Ground
|-
| 2
| SR
|style="background-color:#fe0000; color:#ffffff;"| Secondary Red (Intensity)
| Ground
|-
| 3
| PR
|style="background-color:#9a0000; color:#ffffff;" | Primary Red
|style="background-color:#9a0000; color:#ffffff;" | Red
|-
| 4
| PG
|style="background-color:#009901; color:#000000;" | Primary Green
|style="background-color:#009901; color:#000000;" | Green
|-
| 5
| PB
|style="background-color:#010066; color:#ffffff;" | Primary Blue
|style="background-color:#010066; color:#ffffff;" | Blue
|-
| 6
| SG
|style="background-color:#00fe01; color:#000000;" | Secondary Green (Intensity)
|style="color: white; background: #555;"| Intensity
|-
| 7
| SB
|style="background-color:#0000fe; color:#ffffff;" | Secondary Blue (Intensity)
| ''Reserved''
|-
| 8
| H
| Horizontal sync
| Horizontal sync
|-
| 9
| V
| Vertical sync
| Vertical sync
|}
The original IBM EGA card includes a [[feature connector]] (blue connector J4, see first photo on this page), providing access to two [[RCA connector|RCA connectors]] at the back of card, in addition to several analog and digital signals that the EGA adaptor can be configured to use.<ref>{{Cite book |url=https://minuszerodegrees.net/oa/OA%20-%20IBM%20Enhanced%20Graphics%20Adapter.pdf |title=IBM Enhanced Graphics Adapter |publisher=IBM |date=August 2, 1984 |pages=76–78}}</ref> 

A [[light pen]] interface was also present on the original card.<ref>{{Cite book |url=https://minuszerodegrees.net/oa/OA%20-%20IBM%20Enhanced%20Graphics%20Adapter.pdf |title=IBM Enhanced Graphics Adapter |publisher=IBM |date=August 2, 1984 |pages=84}}</ref>