Boca Systems Complete IDE Series, Manual

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Complete IDE Series: IDE200
3.2 Serial Device Interface (J3, J4)
General Notes: IBM has defined that IRQ4 is assigned to COM1 and
IRQ3 is assigned to COM2; these are needed for interrupt driven
devices such as Mice. In general, serial ports cannot share a common
interrupt, nor can they share the same physical port. COM3 and COM4
are not supported by IBM’s (and most clones’) system BIOS. IBM never
intended COM3 or COM4 to be initialized during boot-up. Your
application software will need to initialize these COM ports.
Serial Device Interface A (J4)
The IDE200 controller is designed using a high speed, AT-type dual
UART NS16450 compatible chip for the serial ports. Serial device
interface “A” has a 9-pin male D-shell connector, and is used to connect
to any asynchronous serial device using a standard EIA RS-232
interface. Examples of such devices are serial printers, plotters, and
modems. Serial port “A” can be set via the J8 jumper for one of the
following three options: