ICC Data (EMV)
What it is
The EMV TLV data of a chip transaction: cryptogram (9F26), AIP (82), TVR (95), unpredictable number, and the rest. Reserved for ISO use (ans ...999) in 1987; ISO 8583:1993 defines it as ICC system related data, b ...255 (up to 255 bytes), the definition card networks follow for chip data.
Format and length shown here are the ISO 8583:1993 definition (b ...255, LLLVAR, up to 255 bytes). ISO 8583:1987 has no ICC field: DE 55 is reserved for ISO use there (ans ...999), and chip data came to it with the 1993 version.
DE 55 carries the chip transaction: BER-TLV encoded EMV tags produced by the card and terminal. The critical ones are 9F26 (Application Cryptogram — the ARQC the issuer validates), 9F27 (cryptogram information data), 82 (AIP), 95 (TVR), 9A/9F21 (date/time), 9F02 (amount), 9F37 (unpredictable number), and 5F34 (PAN sequence). The response carries issuer authentication data (91) and scripts (71/72) back to the card.
Every network wraps the same TLV payload slightly differently (Mastercard DE 55, Visa field 55 usage, some domestic switches use DE 48). Decode the payload with the EMV TLV decoder; validate cryptograms with the ARQC calculator.
Example values
9F2608AABBCCDD11223344 9F2701 80 9505 0000048000ARQC, CID=80 (ARQC requested), and TVR 0000048000: online PIN entered (byte 3) and transaction exceeds floor limit (byte 4).DE 55 on the wire
Bitmap position
DE 55 is bit 55 of the primary bitmap: byte 7, mask 0x02. A primary bitmap with only DE 55 present reads 0000000000000200 in hex.
Length
DE 55 is variable length (LLLVAR): a 3-digit prefix gives the length of the value in bytes, from 0 to 255. A 12-byte value is sent as 012 followed by the value. In ASCII the prefix is the bytes 30 31 32; dialects that pack lengths as BCD send 00 12 instead.
Size in the message
Up to 255 bytes of binary data plus the length prefix. Interfaces that carry binary data as text send each byte as two hex characters, so the value takes up to 510 characters there.
Format b
Format b means binary: raw bytes, often shown or sent as hexadecimal text.
Specification reference
Format and length follow ISO 8583:1993; the rest of the message follows the 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.