The TReadButton structure.

 // ReadButton
 TReadButton    struct
  Result                sbyte  // The function call result, ERR_INVALID_PORT or NO_ERR.
  Index         byte   // The requested button index.
  Pressed     byte   // The returned button state.
  Count         byte   // The returned button pressed count.
  Reset         byte   // If true, the count is reset after reading.
 TReadButton    ends

See the Button name constants group for Index values.