GN_Flr, Read character from filter
Register parameters
RST 20H, DEFW $2809
IN:
IX = filter handle
OUT, if call successful:
Fc = 0
A = character read from filter
Fz = 1, if character is converted, else unconverted, Fz = 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_Flf, flush filter
GN_Flo, open filter
GN_Flw, write character to filter
GN_Fpb, push back into filter