Amstrad PC 2086 dual video output (VGA + monochrome Hercules Graphics Card clone)

Years ago I've heard about a possibility of having two graphics cards installed into one PC-compatible machine, allowing dual video output even on the earliest models. There was one condition though: one of these cards had to be a monochrome Hercules Graphics Card (or its clone), the other card had to be any color graphics card. I've never actually seen this in action until now.

For my experiment, I've removed the network card from my old Amstrad PC 2086, to make a room for a cheap TM6310AR-based monochrome Hercules Graphics Card clone in form of an ISA 8-bit card. I've specifically selected a card that does not contain a secondary parallel port (which was often present on the most popular Hercules Graphics Card clones) as I wanted to avoid a IRQ conflict with the Sound Blaster 2.0 clone card installed into this machine.

The `mode` DOS command allows to switch between the use of the two cards: `mode mono` switches to the Hercules output, while `mode co80` or `mode co40` switches back to the VGA output. A word of warning: this setting survives power down or reboot, so it is better to always switch back to a color mode when finished working with the mono output.

There were various software emulations of CGA graphics card available for the Hercules Graphics Card. On this video I'm presenting one of them, the `simcga` program. It allowed to run early PC games written for the CGA on the monochrome Hercules Graphics Card. Some of those games worked, some not. Two of the working examples are presented here: Hard Hat Mack and Alley Cat. The Hercules Graphics Card was never officially blessed by IBM as it wasn't their design. Therefore, Alley Cat game distributed by IBM was defective when running on a machine on which IBM-recommended graphics card wasn't detected. Hence the game started on Hercules Graphics Card with CGA emulation did not allow to jump into the rooms through the windows. However on this movie the game is fully playable despite being started with the CGA emulation. This is due to the other, IBM-recommended graphics card being detected. Apparently it was sufficient to overcome this artificial limitation.

Amstrad PC 2086 is a late 8086-based PC/XT clone. This one was modified as such:
- 8087 FPU installed
- The MFM disk controller replaced with lo-tech's 8-bit ISA XT-IDE controller (with on-board slot for a Compact Flash card)
- MFM HDD removed; the system is booted from a CF card
- SMC 8003WC 8-bit ISA network card (with RJ-45 connector) installed (removed on this movie to make room for a Hercules Graphics Card clone)
- SoundBlaster 2.0-compatible 8-bit ISA card installed
- Gravis Joystick connected to the game port on the 8-bit ISA SoundBlaster 2.0-compatible card
- Additional RAM installed in form of the lo-tech's 8-bit ISA UMB memory card at 0xD000

The VGA signal from Amstrad PC 2086 was converted to the S-Video signal by the TVOne CS-320R Connect device. The S-Video signal was captured by usbtv video4linux compatible framegrabber.

The Hercules Graphics Card's TTL output was converted to the analog VGA signal by the Monotech PCs EternalCRT (PC TTL to VGA Converter). It allows to select one of the colors to imitate monchrome signal: white, green or amber. I've specifically selected amber as this matches with my very first experience with the PC-compatible computers.