Amex Reader Capabilities Decoder
Decode the Amex ExpressPay Enhanced Contactless Reader Capabilities (tag 9F6E) — the 4-byte bitmap the Kernel 4 reader sends in the GPO command. Amex does not use the TTQ (9F66).
9F6E is kernel-specific: this layout applies to American Express (Kernel 4) only. Mastercard (Kernel 2) uses 9F6E for Third Party Data, Visa for the Form Factor Indicator, Kernel 5 (JCB) for Device Information and Kernel 6 (Discover) for the Form Factor Identifier (Kernel 5 / 6 names per emv-rs).
Sources: EMV Contactless Book C-4 v2.11 Table 4-4 as encoded by openemv/emv-utils. Byte 1 bit 3, byte 4 bits 8–6 and the kernel-version codes (byte 4 bits 3–1) are single source (openemv/emv-utils only). binaryfoo emv-bertlv's older ExpressPay 3.0 layout agrees on the other bits and defines byte 1 bit 2 as "Signature supported", which Table 4-4 leaves RFU.