Appendix B. Service Calls
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## Appendix B. Service Calls

The usb system uses a service call (&80C00) to inform client programs of certain events. Register 0 is used as a reason code. Other registers depend on the reason code.

### Note

Many of these service calls are now considered obsolete and have been superseded by the USB messaging system Appendix D

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Appendix A. Constants | Home | Service_USB 0 - Pipe released