One of many delights of the boring pre-VGA period is that you simply get to specific your creativity with regards to making a random coloration CRT work with an equally thrilling twin CPU laptop just like the DEC Rainbow 100. That is the scenario that the folks over at Usagi Electrical discovered themselves in with a current mission. The Rainbow 100 is an fascinating laptop in that it could boot not solely DOS with its 8088 processor, but additionally CP/M on the Z80 processor. Though typically utilized in monochrome mode, it helps a coloration graphic card to output RGB indicators by way of its male DB15 connector.
Sadly, the goal monitor – a Princeton Ultrasync – featured a feminine DB25 connector that clearly wasn’t going to attach instantly, thus requiring a spot of reverse engineering. Making this very straightforward, the PCB containing the enter connector had the traces clearly marked with the supposed sign, which simply left the mapping of the 2 connectors. One complication right here was with the Rainbow 100 outputting an RGB sign with sync-on-green, whereas the monitor anticipated a separate synchronization sign.
Luckily, most analog screens aren’t significantly fussy as long as they get the anticipated sign someplace within the enter, which simply left the ultimate situation, of the Rainbow 100 outputting the monochrome sign on a particular monochrome pin. This allowed all the pieces to work because it ought to, and leaving these of us who joined the computing period within the 90s recognize of normal VGA cables, apart from for these bizarre Solar and Apple programs with their proprietary connectors.
