EMV Bit Field Decoder

Reading EMV bit numbering

EMV numbers bits from 8 down to 1, where b8 is the most significant bit of a byte and b1 the least. Byte 1 is the leftmost byte of the value. So in a TVR of 0508008000, byte 1 is 05, and the set bits are b3 and b1 — "CDA failed" and a reserved bit.

This is the opposite convention from most programming languages, which is exactly why doing it by hand goes wrong. Every table on this page follows the EMV convention.

Which field is which

TVR (95) is what the terminal thinks went wrong. TSI (9B) is which processing steps actually ran. Read them together: a clear TVR bit means nothing if the corresponding TSI bit says the step never executed.

AIP (82) is the card advertising its capabilities; Terminal Capabilities (9F33) is the terminal advertising its own. Where they disagree, you get the surprising CVM outcomes — a card that supports offline PIN on a terminal that does not will fall through to signature or no CVM.

AUC (9F07) holds the issuer's restrictions on domestic versus international and cash versus goods. When a transaction violates them the terminal sets TVR byte 2 bit 5, "requested service not allowed for card product".

CID (9F27) is one byte that tells you the outcome of a GENERATE AC. The top two bits are the cryptogram type; bit 4 asks for an advice message; the bottom three bits carry a reason code, which is where you find "PIN try limit exceeded" on an offline decline.

Reserved bits

Bits marked RFU are reserved in the spec version cited. Some have since been assigned by newer kernels — relay resistance in TVR byte 5 and on-device CVM in the AIP are recent additions. This tool shows a set RFU bit rather than hiding it, because a set reserved bit usually means one of two things: your data is misaligned by a byte, or you are looking at a kernel newer than the table.

A set bit is not a decline

This is the most common misreading. The TVR is a report, not a verdict. What decides the outcome is whether a set TVR bit overlaps an Issuer Action Code — which is what the IAC comparator is for.