Editing Hercules Graphics Card (section)

== Capabilities ==
[[File:Hercules Graphics Card test image.png|thumb|Wikipedia logo rendered at {{resx|720x348}} without aspect ratio correction]]
[[File:Wikipedia logo on Hercules display (adjusted).png|thumb|Wikipedia logo displayed on a CRT monitor by a Hercules-compatible video card]]
[[File:Hercules graphics simulated image.png|thumb|Hercules image at {{resx|720x348}} without aspect ratio correction]]
[[File:Hercules graphics (aspect ratio corrected).png|thumb|Hercules image with correct aspect ratio as would be seen on a [[Fullscreen (aspect ratio)|4:3 monitor]]]]
The Hercules card provides two modes: 
* {{resx|80×25}} [[text mode]] with {{resx|9×14}} pixel font (effective resolution of {{resx|720×350}}, MDA-compatible)
* {{resx|720×348}} graphics mode (pixel-addressable graphics)<ref name=":0">{{Cite news |last=Pointing |first=Bob |date=June 26, 1989 |title=High-Resolution Standard Is Latest Step in DOS Graphics Evolution |pages=48 |work=InfoWorld |url=https://books.google.com/books?id=lTAEAAAAMBAJ&q=infoworld+1982+hercules&pg=PT47}}</ref>

The text mode of the Hercules card uses the same signal timing as the MDA text mode.

The Hercules graphics mode is similar to the CGA high-resolution ({{resx|640×200}}) two-color mode; the [[Framebuffer|video buffer]] contains a packed-pixel bitmap (eight pixels per byte, one bit per pixel) with the same byte format—including the pixel-to-bit mapping and byte order—as the CGA two-color graphics mode, and the video buffer is also split into interleaved banks, each 8&nbsp;KB in size.

However, because in the Hercules graphics mode there are more than 256 scanlines and the display buffer size is nearly 32&nbsp;KB (instead of 16&nbsp;KB as in all CGA graphics modes), four interleaved banks are used in the Hercules mode instead of two as in the CGA modes. Also, to represent 720 pixels per line instead of 640 as on the CGA, each scanline has 90 bytes of pixel data instead of 80.<ref name="manual101">{{cite book |title=Hercules Graphics Card Owner's Manual |page=16}}</ref>

The 64&nbsp;KB RAM of the HGC can hold two graphics display pages.  Either page can be selected for display by setting a single bit in the Mode Control Register.  Another bit, in a configuration register exclusive to the HGC, determines whether the second&nbsp;32 KB of RAM on the HGC is accessible to the CPU at the base address B8000h.  This bit is reset at system reset (e.g. power-on) so that the card does not conflict with a CGA or other color card at address B8000h.<ref name="manual101b">{{cite book |title=Hercules Graphics Card Owner's Manual |page=3}}</ref>