The Com BRConfig.sys specification allows Business Rules! to support up to eight serial ports. COM must be used to identify the interrupt number and base I/O address of all ports other than COM1 or COM2.
Zero (0) may be used for the COM spec's irq-num (interrupt request number) parameter to indicate that no input interrupt processing should occur. This is useful if the port is to be used only as an output device. Also, COM may now be specified with the CONFIG command.
Since there are about as many ways to support additional ports as there are manufacturers of serial port boards, programmers are responsible for determining the feasibility of individual boards and configuring them to operate. The boards must support the IBM-PC standard for I/O port usage, and the settings must not conflict with other serial ports already in the system.
COM1 4 3F8 COM2 3 2F8
The COM keyword must be immediately followed by the "num" parameter, which represents a digit from 1 to 8.
The "irq-num" parameter represents an interrupt request number from 2 to 15. According to the IBM-PC standard, 4 is assigned to COM1 and 3 is assigned to COM2. Other numbers within the 2-15 range may be used if you are absolutely certain that the interrupt is not used and that it is supported on your machine. In general, 2, 3, 4 and 7 are available -but you should use caution with 2 and 7. More than one (or all) COM ports may be assigned to the same interrupt. When that interrupt occurs, all ports using the interrupt are checked.
"Base I/O address" represents the starting I/O address of the port. Each port is assigned eight contiguous I/O addresses; the base address is the first of these eight. The IBM-PC standard uses 3F8-3FF for COM1 and 2F8-2FF for COM2.
- 1.) COM may be specified with the CONFIG command.
- 2.) The values for COM1 and COM2 may be reassigned.
- 3.) The COM3 through COM8 ports have defaults of zero: they are undefined. Attempts to open them without defining them will result in a 4152 (File not found) error.