Technical information

Serial Solutions What To Do First
Interrupt lines for COM3 onwards must be passed to the
NEWCOM.SYS driver by the /In,i parameter.
Where n specifies the COM port, n may only be a single port
NOT a range of ports.
And i is the interrupt line, in the range 2 to 15, used by the
port. If i is -1 then this port does not use interrupts. For
example:-
/I3,10 COM3 is using interrupt line 10
/I4,11 COM4 is using interrupt line 11
/I5,7 COM5 is using interrupt line 7
/I6,5 COM6 is using interrupt line 5
/I7,12 COM7 is using interrupt line 12
/I2,-1 COM2 is not using interrupts (won’t work well with
Serial Solutions)
Multiport Serial Cards._____________________
Each serial port we have discussed so far has required its
own interrupt line if we want trouble free communications with
external devices. As more serial ports are added a fundamental
limit of the PC expansion bus slot is reached, there are only 11
interrupts lines available. Of the 16 interrupt line in the PC
design only 11 are brought out to the expansion slots, the other
5 are used internally for timers, maths coprocessors etc. The 11
on the slot are reduced to 9 in practice since the floppy disk and
the hard disk require one each. If network, SCSI or sound cards
are added even less interrupts are available.
It soon seems impossible to add an 8 port card to a PC
that already has COM1 and COM2 installed.
To get over the limiting factor of the number of interrupts
available many multiport cards have special circuitry on board
that allows the ports on the card to share a single interrupt
between themselves.
Two interrupt sharing mechanisms have become popular
and both these are supported by Serial Solutions.
Page 8 Chapter 1