Many subsystems that I have integrated over the years have used the trusty RS-232 standard. While this is great for us engineers (since RS-232 is pretty easy to work with), it can be a pain for our customers as systems have started dropping these legacy ports. We started using Apple Mac Minis due to their low cost and availability. These systems have dispatched completely with legacy ports due to their form factor and forward looking designs. Initially during prototyping work we attempted to get by with commercially available off the shelf USB to RS-232 adapters. Many of these devices were designed around the Prolific 2303 chipset. We found a number of shortcomings with these devices. These controllers were unable to maintain high levels of utilization (i.e. from GPS receivers, or laser range finders). Additionally, in an attempt to cut costs the manufacturers omitted the EEPROM configuration memory from their designs. This led to the quirk of plugging the same controller into a different port caused a new COM port to be assigned to it. This complicated system maintenance and software design by having to allow for quick user changeable configurations. To address this problem I designed a two port serial adapter based on the FTDI FT2232 devices. We included the EEPROM configuration memory to eliminate one of the shortcomings of the commercial available solutions. The FTDI chipsets do not exhibit the same problems at high utilization as the Prolific chipsets. Below are a couple of scans of the controllers.
USB to RS-232 Adapter (Top)
USB to RS-232 Adapter (Bottom)