Impulse 3055 - Manual (Page 7)

Card Setup
Sealevel Systems ULTRA-485 Page 4
Interrupt Modes
Header E2 selects the interrupt mode for the ULTRA 485.
‘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.
Figure 2 - Header E2, Normal IRQ Mode
Set the jumper to ‘S’ if you are using more than one ULTRA 485 in a bus or to
completely remove the pull-down resistor for hardware compatibility. Setting
the adapter in this configuration when it is not accompanied by a pull-down
resistor will prevent the ports from triggering an interrupt.
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 485 or a compatible adapter in a bus you should only have one port set
to ‘M’. The following example shows two ULTRA 485 adapters sharing a
single IRQ.
Figure 3 - Header E2, Shared IRQ Mode