User`s manual

98, ME, NT, 2000 and XP may limit your IRQ selection without aftermarket drivers. This is
usually not required unless all IRQ’s supported by the OS are already allocated.
Note
PC/104 CPU manufacturers vary in implementation of the interrupt interface. Most use pull-
ups on the interrupts. This allows a board to drive low or tristate float high the interrupt lines
preventing damage if two boards conflict. The PCFW-104 uses the tristate scheme. On a few
motherboards the manufacturers use pulldown resistors. The PCFW will not request a inter-
rupt in this scheme since the tristated line cannot float high. In this case a pad is provided
for installation of a pullup resisitor, R8. The user should install a 1K 0805 resistor on this pad.
Should this not work the largest value possible should be used to prevent excessive current
draw. 250 ohms is a recommended minimum
Address Select Jumpers, JP2
For flexibility with most SW and Development libraries this unit will support any valid address
between 0x000-0x007 and 0x7F8-0x7FF.
Most applications will use one of the common serial port addresses. The most common are:
COM1 = 3F8, IRQ4, COM2 = 2F8, IRQ3 COM3 = 3E8, IRQ4 COM4 = 2E8, IRQ3
Most software development libraries for serial communication support non-standard address
and/or IRQ assignments.
An excellent library is the COMM/DRV LIB from Willies Computer Software at http://www.
wcscnet.com/.
The default address is 3E8 which is COM3. To select the address you desire place jumpers on
JP2 in the following order.
From left to right. Placing a jumper sets the address bit to 0 or low.
Addressing Examples
Hex A10 A9 A8 A7 A6 A5 A4 A3
2F8 X X
300 X X X X X X
310 X X X X X
3E8 X X
3F8 X
7F8
X = jumper installed meaning bit = 0.
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