CM312 Datasheet, PDF (34/56 Pages) List of Unclassifed Manufacturers – Communications utilityModule

Interrupt Sharing
Interrupt sharing is a mechanism which allows different devices sharing same active high IRQ lines
on the PC/104 bus, given that there is a interrupt sharing circuit associated with each device. The
utilityModule provides interrupt-sharing circuits for all the serial ports; thus it allows sharing of
one IRQ line among the serial ports in the utilityModule. However, user needs to be careful to
share an IRQ line with devices in the system elsewhere, and be sure that other devices also share
their IRQ lines as well. For instance, users should be aware of that the IRQ3/IRQ4 associated with
serial port J3/J4 on RTDUSA cpuModule are not shareable. And if the utilityModule is in the
same system with RTDUSA cpuModule, be advised not to use/share IRQ3/IRQ4 for the
utilityModule unless you have serial ports on the cpuModule disabled.
Interrupt sharing in a PC/104 system requires one 1K pull-down resistor per IRQ line for all the
devices that share the IRQ. Installing a G jumper in the utilityModule will pull its associated IRQ
line down with 1K resistor. That is, for example, if IRQn is shared among four serial ports on the
utilityModule, only one G jumper needs to be installed for IRQn line. If more than one G jumper
are installed, the pull-down on IRQn line will be much stronger that expected 1K ohm, which will
prevent interrupt controller from functioning correctly.
Let consider two cases to demonstrate the concepts for the above discussion. Let us assume that
IRQ5 and IRQ10 are not used and driven by other devices in the system. For the first case, IRQ10
line is shared among the four serial ports and for the second case IRQ5 is shared for port 1 and
port 2, while IRQ10 is shared among port 3 and port 4.
The following two tables listed the interrupt jumper settings for each case respectively.
Table 11 Jumper Settings for interrupt sharing Case 1
Jumper
JP1
G jumper
JP2
G jumper
JP3
G jumper
JP4
G jumper
Setting
13-14
Installed
13-14
Removed
13-14
Removed
13-14
Removed
Function
IRQ10 for 1^st COM port
1K pull down resister added on IRQ10
from PORT1
IRQ10 for 2^nd COM port
No pull down resister added on IRQ10
from PORT2
IRQ10 for 3^rd COM port
No pull down resister added on IRQ10
from PORT3
IRQ10 for 4^th COM port
No pull down resister added on IRQ10
from PORT4
CM312 Quad Serial utilityModule
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RTD Embedded Technologies, Inc.