83Plus:Hooks:9BD4

Synopsis

Name: USB Activity Hook

Hook Pointer Block Address: 9BD4

Hook Enable BCALL: 528A

Hook Disable BCALL: 528D

Hook Call BCALL: (none known)

Hook Active Flag: 0, (iy+3Ah)

This hook is called from the interrupt routine when USB activity is detected.

Using the Hook

• The hook is called whenever any of bits 4-0 of port 55h are low.
  • C holds the complement of these bits.
• B always contains the constant 2Ch.
• Return Zero flag to abort linking.

Comments

This hook was introduced in OS 2.30. Apps should check the OS version before attempting to use this hook.

Credits and Contributions

• 84plusfreak (Sernin van de Krol) discovered and analyzed this hook.