Hello. I've found the mapping in the present viscii.ucm have a bit diffrence from that in RFC 1456.
U+1EA8 (<A^?> in VIQR) should be mapped for 0x86, and U+1EA9 (<a^?> in VIQR) for 0xA6. Here is a test scratch to check whether VISCII indeed supports all the Latin extensions for Vietnamese, i.e. U+1EA0..U+1EF9. #!perl for (my $u = 0x1EA0; $u <= 0x1EF9; $u++) { my $e = encode("VISCII", chr $u, Encode::FB_WARN); } warn "End."; __END__ --- viscii.ucm~ Thu Feb 06 10:52:18 2003 +++ viscii.ucm Sun Feb 16 11:45:00 2003 @@ -143,6 +143,7 @@ <U1EB6> \x83 |0 # LATIN CAPITAL LETTER A WITH BREVE AND DOT BELOW <U1EA4> \x84 |0 # LATIN CAPITAL LETTER A WITH CIRCUMFLEX AND ACUTE <U1EA6> \x85 |0 # LATIN CAPITAL LETTER A WITH CIRCUMFLEX AND GRAVE +<U1EA8> \x86 |0 # LATIN CAPITAL LETTER A WITH CIRCUMFLEX AND HOOK AB OVE <U1EAC> \x87 |0 # LATIN CAPITAL LETTER A WITH CIRCUMFLEX AND DOT BELOW <U1EBC> \x88 |0 # LATIN CAPITAL LETTER E WITH TILDE <U1EB8> \x89 |0 # LATIN CAPITAL LETTER E WITH DOT BELOW @@ -174,7 +175,7 @@ <U1EB7> \xA3 |0 # LATIN SMALL LETTER A WITH BREVE AND DOT BELOW <U1EA5> \xA4 |0 # LATIN SMALL LETTER A WITH CIRCUMFLEX AND ACUTE <U1EA7> \xA5 |0 # LATIN SMALL LETTER A WITH CIRCUMFLEX AND GRAVE -<U1EA8> \xA6 |0 # LATIN CAPITAL LETTER A WITH CIRCUMFLEX AND HOOK ABOVE +<U1EA9> \xA6 |0 # LATIN SMALL LETTER A WITH CIRCUMFLEX AND HOOK ABOVE <U1EAD> \xA7 |0 # LATIN SMALL LETTER A WITH CIRCUMFLEX AND DOT BELOW <U1EBD> \xA8 |0 # LATIN SMALL LETTER E WITH TILDE <U1EB9> \xA9 |0 # LATIN SMALL LETTER E WITH DOT BELOW regards, SADAHIRO Tomoyuki