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© Sealevel Systems, Inc. 3405 Manual | SL9144 6/2021
Card Setup, Continued
Jumper Selections
For ease of configuration, the headers are grouped by port. Port one headers have a ‘J1’ prefix, Port two
headers have the ‘J2’ prefix, etc. For example, the header that controls the Port one IRQ selection is J1B,
the header that controls the Port 2 IRQ selection is J2B. The silk-screen also provides information for
configuring the adapter without the use of the manual. This is particularly useful in field re-configuration.
IRQ Selection
Headers J1B through J4B 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. (This only applies to the traditional DOS COM: port assignments, in Windows COM1: can use
I/O address 300 and IRQ15 if it is available!)
Figure 4
–
Headers J1B
–
J4B, IRQ Selection
Most DOS 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
.
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 J1A through J4A. When sharing IRQs, many operating systems (i.e., Windows
NT) will require the location of the
I
nterrupt
S
tatus
P
ort (
ISP
). Please see Page 10 for a description of the
ISP and how it is used.
3 4 5 6 7
10 11 12 15
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