=> R1 = &43 (reason code)
R2 = 8 (sub reason code)
R3 = alphabet number
<= R1 = 0 if claimed, preserved otherwise
R4 = pointer to table if recognised, else preserved
R2-R3 preserved
Any module providing additional alphabets should check to see if it can provide a conversion table for the given alphabet number. If it can, it should claim the service and return a pointer to the table in R4, otherwise return with all register preserved.
The table has 256 32-bit entries, one for each character, giving the equivalent UCS code. If a character is not defined in the alphabet, its entry should contain &FFFFFFFF (not a valid UCS character).
Characters 0-31 and 127 are control codes in RISC OS - their entries in the tables of all alphabets should be 0-31 and 127 to guarantee a sensible translation to UTF8.
It is nonsensical to issue this service call for alphabet UTF8 (111). No module should claim such a call.
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