6.2 Interrupt Status Register
The DS-200/300 is equipped with an Interrupt Status Register (ISR) which
can be used to simplify the servicing of shared interrupts. This register is
located at [base 7] along with the Options Register. Like the OR,
the SP jumper must be removed to access the ISR. To further indicate an
access to this register, the DLAB bit in the LCR of the UART must be set to
0. The ISR is read-only.
When a hardware interrupt occurs, reading the ISR will return the
interrupt status of both ports on the DS-200/300, as shown in Figure 14.
Individual bits are cleared as the interrupting ports are serviced. The
interrupt service routine must ensure that the ISR reads zero before
exiting, or the DS-200/300 will be unable to signal subsequent interrupts.
Serial 0 --- 1 if interrupt pending
0
Serial 1 --- 1 if interrupt pending
1
0 (not used)
2
0 (not used)
3
0 (not used)
4
0 (not used)
5
0 (not used)
6
0 (not used)
7 (MSB)
DESCRIPTION
BIT
Figure 14 --- Interrupt Status Register contents
DS-200/300 User's Manual
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