CM312 datasheet(34/56 Pages) ETC

34 / 56 page

CM312 Quad Serial utilityModule

RTD Embedded Technologies, Inc.

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

Setting

Function

JP1

G jumper

13-14

Installed

IRQ10 for 1

st COM port

1K pull down resister added on IRQ10

from PORT1

JP2

G jumper

13-14

Removed

IRQ10 for 2

nd COM port

No pull down resister added on IRQ10

from PORT2

JP3

G jumper

13-14

Removed

IRQ10 for 3

rd COM port

No pull down resister added on IRQ10

from PORT3

JP4

G jumper

13-14

Removed

IRQ10 for 4

th COM port

No pull down resister added on IRQ10

from PORT4

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