Appendix
Appendix
User's Manual
BAB 740
7—1
7 Appendix
7.1
Description of On-board Devices
This chapter describes how the on-board devices are accessed by
operating system drivers. When an operating system, such as OS-9
and VxWorks, is used, there should be no need to address these
devices with user-written code.
7.1.1 SMI Ticker
The output of counter/timer 2 of the W83C553F may be routed to the
System Management Interrupt input of the CPU when J1701 is set to
position 7-8. This can be used to generate a periodic interrupt with
higher priority than normal interrupts. A negative edge of the PC-
Speaker output triggers the SMI when enabled via bit 7 of I/O
address $809.
Writing to I/O address $808 clears the SMI.
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