Category Archives: Virtual hardware

Emulating the 8250 UART in software

Starting with build A775, the PC emulation software contains a fairly complete implementation of a virtual 8250 UART chip for RS-232 communication. It supports both the INT 14h interface and direct access to 0x3F8-0x3FF ports, which are translated, via the inter-processor call mechanism, to appropriate Commodore KERNAL calls and 6551 ACIA chip accesses. The implementation… Read More »

No, it’s not a CGA video card

Commodore CBM-II computers have rather limited video capabilities – they can only output monochrome 80×25 text. The only PC video hardware that can be reasonably emulated with this is the text-only Monochrome Display Adapter. The MDA (and its descendant Hercules) is peculiar in that its video buffers are located in a different memory area than… Read More »

Emulating PC hardware in software

To achieve the goal of making the machine PC-compatible, it is necessary to pretend that it has a set of PC peripherals present, such as the 8253 PIT, 8250 UART, the 6845 CRTC from the MDA card, and so on. Unfortunately, the Commodore CBM-II has none of these. What is one supposed to do then?… Read More »