Impulse 3189 - Manual (Page 6)

Card Setup
Sealevel Systems ULTRA-SIO Page 3
IRQ Selection
Headers E11 and E12 select the interrupt request for each serial port. If COM1: is selected, the corresponding
jumper must be on the IRQ4 setting. If COM2: is selected, the corresponding jumper must be on IRQ3.
Note: Most communications software applications default COM3: to IRQ4 and COM4: to IRQ3. This requires the
sharing of interrupts between COM1: and COM3:, and between COM2: and COM4:. While this is the default,
it is not always the preferred setting. Check your software configuration instructions to determine the most
appropriate IRQ selection.
15 14 12 11 10
7 6 5 4 3
2/
9
Figure 2 - Header E11 and E12, IRQ Selection
Any two or more ports can share a common IRQ by placing the jumpers on the same IRQ setting at header E11 and
E12 and setting the appropriate selections at E5 and E6. Note that a polling type driver is needed to share interrupts
in this fashion. Windows does not supply a polling type driver. Consult your particular software for IRQ selection. If
no interrupt is desired, remove the jumper.
Interrupt Modes
Header E5 and E6 selects the interrupt mode for each port. Each port must be set in the correct mode to insure
proper operation.
‘N’ indicates the (N)ormal, single interrupt per port mode. ‘S’ Indicates the (S)hared interrupt mode, which allows
more than one port to access a single IRQ. Any two or more ports can share a common IRQ by placing the jumpers
on the same IRQ setting and setting the appropriate selections at E1. Consult your particular software for IRQ
selection. If no interrupt is desired, remove the jumper. ‘M’ indicates the inclusion of a 1K ohm pull-down resistor
required on one port when sharing interrupts.
1
2
N S M
E5
E6
Figure 3 - Header E5 & E6, Normal IRQ Mode
Set the jumpers to ‘S’ for shared interrupt mode on all blocks sharing an IRQ except one. Set that port block for ‘M’.
This provides the pull-down resistor circuit that makes sharing IRQs possible. If you are using more than one Ultra-
SIO or a compatible adapter in a bus you should only have one port set to ‘M’. The following example shows both
ports sharing a single IRQ.