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6.1 Interrupt Sharing
Both ports on the DS-100 can share the same interrupt level or they can share their interrupt with
another Quatech adapter supporting sharable interrupts. Jumper J2 can be used to connect the
UART generated interrupt directly to the selected IRQ or to enable the interrupt sharing circuit.
In either case, the software driving the serial ports must determine which port or ports are
requesting service when an interrupt is generated. To maintain 100% ISA bus compatibility, J2
should be set in the non-sharable mode. If non-sharable mode is selected for both ports, the user
must ensure that each port is using a unique IRQ.
J2 --- Sharable interrupt
1
1
4
4
2
2
5
5
3
3
6
6
1
4
4
1
2
5
5
2
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6
6
3
Serial 0 non-sharable
Serial 1 non-sharable
Serial 0 non-sharable
Serial 1 sharable
Serial 0 sharable
Serial 1 non-sharable
Serial 0 sharable
Serial 1 sharable
jumper block configurations
(default)
Figure 10--- Sharable interrupt selection
The DS-100 signals a hardware interrupt when any port requires service. The interrupt signal is
maintained until no port requires service. Because the ISA bus is edge-sensitive, this behavior
forces the interrupt service routine to ensure that all ports are checked before exiting. A way to
do this is to poll each port until an interrupting port is found. After servicing the port, all ports
should be checked again. If any interrupting port is left unserviced the DS-100 will be unable to
signal any further interrupts.
5-2 Quatech Inc.