GN_Flw, write character to filter

RST 20H, DEFW $2609

IN:

     IX = filter handle
     A = character to write to filter

     Fc = 0
     A = A(in)

     Fc = 1
     A = error code:
          RC_HAND ($08), bad filter handle
          RC_FLF ($0A), filter is full

     A.BCDEHL/IXIY same
     .F....../.... different

Bugs:
 

Related calls:

GN_Flc, close filter
GN_Flf, flush filter
GN_Flo, open filter
GN_Flr, read from filter
GN_Fpb, push back into filter