TTQ Decoder

What the Terminal Transaction Qualifiers (9F66) tell the card

The Terminal Transaction Qualifiers (TTQ), EMV tag 9F66, is a 4-byte bitmap a contactless reader hands to the card at the very start of a tap. It is the terminal's opening statement: which interfaces and transaction modes the reader supports (mag-stripe, qVSDC/EMV, contact chip), whether it can go online, and which cardholder verification methods — online PIN, signature, or consumer-device CVM — it is prepared to honour. The card reads these bits and decides how to respond, so a single wrong bit can change the entire authorisation path.

In a Visa qVSDC tap the TTQ travels in the PDOL data of the GPO command; the card answers with its own Card Transaction Qualifiers (9F6C), not with a TTQ. The value sent is not always the configured one: Entry Point pre-processing (Book B) starts from the configured TTQ, first clears "Online cryptogram required" and "CVM required" (byte 2 bits 8 and 7), then sets each of them again for this transaction when its condition is met — depending on the amount and the reader limits. That is why a trace can show a different TTQ from the terminal configuration.

Why this tag is kernel-specific

Unlike most EMV tags, 9F66 does not have one universal layout. The same four bytes are interpreted differently depending on the contactless kernel:

• Visa, Kernel 3 (VCPS / qVSDC) — the original and most common layout.
• Discover, Kernel 6 (D-PAS) — adds Fast Mode and Transit terminal bits (single source: openemv/emv-utils).
• UnionPay, Kernel 7 (QuickPass) — the shared layout except byte 1 bit 7, which Book C-7 reserves for proprietary use, plus byte 4 bit 8 for fDDA v1.0 support (single source: openemv/emv-utils notes on C-7).

Mastercard (Kernel 2), American Express (Kernel 4) and JCB (Kernel 5) do not use a TTQ — they carry equivalent capability flags in their own kernel data. In Kernel 2 data, tag 9F66 is a different object altogether: PUNATC(Track2), 2 bytes. Decoding a Mastercard tap against the Visa layout is one of the most common analysis mistakes, which is why this decoder asks you to pick the kernel first.

How to read the breakdown

Each byte is shown with its set (●) and cleared flags. Byte 1 is mostly about reader capability — what the terminal can do — while byte 2 carries requirements that force a behaviour, such as "Online cryptogram required" or "CVM required". If byte 2 demands an online cryptogram, an offline-only card will decline; if it demands CVM, the card must present a verification method the terminal supports. Reading bytes 1 and 2 together usually explains why a tap went online, fell back, or asked for a PIN. Bits that the selected kernel leaves RFU are flagged when set — for Visa that includes byte 1 bit 7 (labelled "VSDC supported" in early VCPS versions and in some older decoders) and all of byte 4.

Bit definitions follow EMVCo Book C-3 (Visa/Kernel 3), Book C-6 (Discover/Kernel 6) and Book C-7 v2.11 (UnionPay/Kernel 7). All decoding happens locally in your browser — nothing you paste here is transmitted or stored.