 HGC with parallel port | |
| Release date | 1982; 43 years ago (1982) |
|---|---|
| Architecture | Motorola 6845 |
| Cards | |
| Entry-level | Hercules Graphics Card |
| Mid-range | Hercules Graphics Card Plus |
| High-end | Hercules InColor Card |
| History | |
| Predecessor | MDA,CGA |
| Successor | Enhanced Graphics Adapter |
TheHercules Graphics Card (HGC) is a computergraphics controller formerly made byHercules Computer Technology, Inc. that combinesIBM'stext-onlyMDA display standard with abitmapped graphics mode, also offering aparallel printer port.[1][2] This allows the HGC to offer both high-quality text and graphics from a single card.
The HGC was very popular and became a widely supportedde factodisplay standard onIBM PC compatibles. The HGC standard was used long after more technically capable systems had entered the market, especially ondual-monitor setups.
The Hercules Graphics Card was released to fill a gap in the IBM video product lineup. When theIBM Personal Computer was launched in 1981, it had two graphics cards available: theColor Graphics Adapter (CGA) and theMonochrome Display And Printer Adapter (MDA). CGA offered low-resolution (320 × 200) color graphics and medium-resolution (640 × 200) monochrome graphics, while MDA offers a sharper text mode (equivalent to720 × 350) but has no per-pixel addressing modes and is limited to a fixedcharacter set.
These adapters were quickly found to be inadequate by the market, creating a demand for a card that offers high-resolution graphics and text.[3] The founder ofHercules Computer Technology, Van Suwannukul, created the Hercules Graphics Card so that he could work on hisdoctoral thesis on anIBM PC using theThai alphabet, impossible with the low resolution of CGA or the fixed character set of MDA.[4] It initially retailed in 1982 for $499.[5]
The original HGC is an8-bit ISA card with 64 KB ofRAM, visible on the board as eight 4164 RAM chips, and aDE-9 output compatible with theIBM monochrome monitor used with the MDA. Like the MDA, it includes a parallel interface for attaching a printer.[1]
The video output is 5 VTTL, as with the MDA card.[6][7][8] Nominally, the Hercules card provides a horizontal scanning frequency of 18.425 ± 0.500 kHz and 50 Hz vertical.[9] It runs at two slightly different sets of frequencies depending on whether in text or graphics mode, providing a different vertical refresh rate and a different aspect ratio via a different pixel clock and number of scanlines.[citation needed]
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The Hercules card provides two modes:
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 (640 × 200) two-color mode; thevideo 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 KB in size.
However, because in the Hercules graphics mode there are more than 256 scanlines and the display buffer size is nearly 32 KB (instead of 16 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.[11]
The 64 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 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.[12]
In text mode, the HGC appears exactly like an MDA card.[13] Graphics mode requires new techniques to use. Unlike the MDA and CGA, thePC BIOS provides no intrinsic support for the HGC. Hercules developed extensions, calledHBASIC, forIBM Advanced BASIC to add HGC support[14] and Hercules cards came withGraph X, asoftware library for Hercules graphical-mode support andgeometric primitives.[13]
Popular IBM PC programs such asLotus 1-2-3 spreadsheet,[13]AutoCAD computer-aided drafting,PageMaker andXerox Ventura desktop publishing, andMicrosoft Flight Simulator 2.0 came with their own drivers to use the Hercules graphics mode.[15]
Though the graphics mode of the Hercules card is not CGA-compatible, it is similar enough to the two CGA graphics modes that with the use of third-partyterminate-and-stay-resident programs it can also work with programs written for the CGA card's standard graphics modes. As the Hercules card does not actually have color-generating circuitry, nor can it connect to a color monitor, color appears as simulated grayscale in varyingdithering patterns.[16][17][18]
Clones of the Hercules appeared, including generic models at very low prices, usually without the printer port. Hercules advertisements implied that use of generic Hercules clones can damage the monitor.[19]
The Hercules Graphics Card was very successful, especially after Lotus 1-2-3 supported it, with one-half million units sold by 1985. As of June 1986[update] Hercules Computer Technology had 18% of the graphics card market, second to IBM.[20] Hercules-compatible graphics cards shipped as standard hardware with mostPC clones. As ade facto standard, support in software was widespread.[10]
The Hercules Graphics Card had several versions.
Several updated versions of the originalHercules Graphics Card exist. The original board from 1982 is referenced asGB100, with updated versions in 1983 (GB101), 1984 (GB102) and 1988 (GB102Z).[21]
TheHercules Graphics Card Plus orHGC+ (GB112) was released in June 1986 at an original retail price of $299.[22] It was an enhancement of the HGC, adding support for redefinable fonts called RAMFONT inMDA-compatible text mode.[23] It was based around a specialty chip designed by Hercules Computer Technology, unlike the original Hercules Graphics Card, which used standard components.[24] Software support includedLotus 1-2-3 v2,Symphony 1.1,Framework II andMicrosoft Word 3.[22]
In 1988 Hercules released theHercules Network Card Plus, (HNC NB112) a variant of the Graphics Card Plus with an integratedTOPS/FlashTalk-compatible network adapter.[25] Like the HGC+, it supported RAMFONT, but lacked a printer port.[26][27][28]
TheInColor Card (GB222) was introduced in April 1987. It included color capabilities similar to theEGA, with 16 colors from a palette of 64. It retained the same two modes (80 × 25 text with redefinable fonts and720 × 348 graphics), and was backward-compatible with software written for the earlier monochrome Hercules cards.[29][30][31][32][33]
TheHercules Color Card (GB200) was a CGA-compatible video board and should not be confused with the InColor Card.[34] This board could coexist with the HGC and still allow both graphics pages to be used.[35] It would detect when the second graphics page was selected and disable access to its own memory, which would otherwise have been at the same addresses. A version without printer port exists[36]
TheHercules Text Card was a text-only MDA clone, but offered a parallel printer port.[37]
Other boards offered Hercules compatibility.[38]
Certain later models of theTandy 1000 (such as the 1000 TL and SL) and theEpson Equity[40] contained circuitry built into their CPU boards that supported Hercules display modes in addition to their standard CGA modes.
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