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 with B=0 to abort linking, similar to the silent link hook.

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.