GN_Flf, Flush filter
Register parameters
RST 20H, DEFW $2A09
IN:
IX = filter handle
OUT, if call successful:
Fc = 0
A = character from filter
Fz = 1, if character is converted, else 0
OUT, if call failed:
Fc = 1
A = error code:
RC_HAND ($08), Bad filter handle
RC_EOF ($09), Filter is empty
Registers changed after return:
..BCDEHL/IXIY same
AF....../.... different Related calls
GN_Flc, close filter
GN_Flo, open filter
GN_Flr, read from filter
GN_Flw, write character to filter
GN_Fpb, push back into filter