Quatech DS-100 user manual Interrupt Sharing

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.

1	4	1	4
2	5	2	5
3	6	3	6

Serial 0 non-sharable		Serial 0 non-sharable
Serial 1 non-sharable
		Serial 1 sharable
	(default)
1	4	1	4
2	5	2	5
3	6	3	6
Serial 0 sharable		Serial 0 sharable
Serial 1 non-sharable		Serial 1 sharable

J2 --- Sharable interrupt

jumper block configurations

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.