Additional Response Data
What it is
Supplementary response information — AVS results, CVV2 results, and network-specific response detail.
DE 44 on the wire
Bitmap position
DE 44 is bit 44 of the primary bitmap: byte 6, mask 0x10. A primary bitmap with only DE 44 present reads 0000000000100000 in hex.
Length
DE 44 is variable length (LLVAR): a 2-digit prefix gives the length of the value in characters, from 0 to 25. A 12-character value is sent as 12 followed by the value. In ASCII the prefix is the bytes 31 32; dialects that pack lengths as BCD send 12 instead.
Size in the message
At most 27 bytes when the message travels as text (ASCII or EBCDIC), or 26 bytes in binary dialects that pack the length prefix as BCD.
Format an
Format an means alphanumeric: letters and digits.
Specification reference
Defined in ISO 8583:1987 (base). Card networks publish their own dialect tables (Visa BASE I / V.I.P., Mastercard CIS) that refine formats, lengths, and — for private-use elements — the entire layout. Always confirm against the interface specification you implement.