Manual Number: 00750-006-5
Page 4
ULTRA-485 Manual
Interrupt Modes
Header E2:
This header selects the interrupt mode for the ULTRA-485.
“
N
” indicates the (
N
)ormal, single interrupt per port mode. This setting is the normal setting for most
applications.
The “
S
” indicates the (
S
)hared interrupt mode . Set jumpers to “
S
” for shared interrupt mode for all
ports sharing an IRQ except for one. Set one of the ports sharing an IRQ to “M”. This provides the
pull-down resistor circuit that makes sharing of IRQ’s possible. This is the preferred Windows and
OS/2 setting. 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 3: 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
.
The following example shows two ULTRA-485 adapters sharing a single IRQ.
Figure 4: Header E2, Shared IRQ Mode
NOTE:
If you are using more than one ULTRA-485 or a compatible card in a bus sharing a single
interrupt, you should only have on port set to "M".
