Z88 Developers' Notes
Contents   Contents of System Calls

OS_Fn, miscellaneous OS functions

RST 20H, DEFB $7B

IN: 

     A = FN_AH ($01), allocate handle
          B = handle type
          B = 0, does not allocate a handle properly - the next handle is
          given the SAME number
OUT, if successful: 
     Fc = 0
     IX = handle
OUT, if failed: 
     Fc = 1
          A = RC_ROOM
Registers changed after return: 
     ..BCDEHL/..IY same
     AF....../IX.. different


IN:
      A = FN_VH ($02), verify handle
          B = handle type
          IX = handle
OUT, if successful: 
     Fc = 0
OUT, if failed 
     Fc = 1
          A = RC_ROOM
Registers changed after return: 
     ..BCDEHL/IXIY same
     AF....../.... different


IN:
     A = FN_FH ($03), free handle
          B = handle type
          IX = handle
OUT, if successful: 
     Fc = 0
     IX = 0
OUT, if failed: 
     Fc = 1
          A = RC_HAND
Registers changed after return: 
     ..BCDEHL/..IY same
     AF....../IX.. different
Notes:
Internal operating system usage.
This call is probably used to allocate all I/O type handles. The handle type is unfortunately undocumented.