1.2 Device Implementation Considerations
The solution of the COM device identification problem addresses major concerns of end-users, system integrators, and operating system vendors. It also presents an excellent business opportunity for providing measurable value and differentiation in the short term, by reducing the user difficulties and associated technical support costs.
There are two ways that serial device manufacturers can implement this specification. For simple hardware based devices (e.g. serial mice) the hardware (e.g. ASICs) will need revision. For intelligent serial devices (e.g. modems and printers) these changes can be implemented by controller code firmware changes. However, care has to be taken in the controller code to avoid false-positive (erroneous) detection of the COM Enumerator (confusing the application software with unexpected PnP ID) or failure to detect the COM Enumerator.
Note that for devices that are logically serial but are installed in a PC system bus, particularly ISA, EISA, MCA (MicroChannel Architecture) or PCMCIA modems, the requirements of the appropriate bus Plug and Play specification must be met for Plug and Play compatibility. Otherwise, important bus resources (address space, Interrupts, DMA, etc) cannot be allocated by the Plug and Play system software, and resource collisions may result, negating the value of Plug and Play.
However, if a bus based COM device does meet the requirements of ISA Plug and Play, then the requirements of COM Plug and Play are optional. For example, an ISA-bus internal modem must support ISA Plug and Play; if it does, COM Plug and Play is not required, although it might provide useful additional information.