AH = 81h: Unlock Card Port

This function unlocks a card port which has been previously locked by function 80h. Prior to unlocking, all the mapped pages of the port must be unmapped.

This function is intended to be used by the XIP loader's exit processing so that the card port will be available for use by other programs.

• Input: AH = 81h
  DX = port number to unlock

• Output: AH = Completion Status
  00h = Success (No Error)
  A0h = Error - Invalid port number
  A1h = Error - Port not locked
  A3h = Error - Port has mapped pages

• Error conditions: As given in AH
• Registers modified: AH