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6.1 Interrupt Sharing
Both ports on the DS-200/300 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.
J2 --- Sharable interrupt
1
1
4
4
2
2
5
5
3
3
6
6
1
4
4
1
2
5
5
2
3
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
Figure 13--- Sharable interrupt selection
The DS-200/300 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-200/300 will be unable to
signal any further interrupts.
DS-200/300 User's Manual 6-2