Data encoding specification

Alipay+ NFC SDK supports ASCII and BCD encoding modes. If you provide custom data, you must pass it as a 20-character hexadecimal string representing 10 bytes of raw data. The SDK then encodes this data based on the selected encoding mode.

Specifications	ASCII mode	BCD mode
Supported characters	`0-9`, `A-Z`, `a-z`, `@`, `#`	`0-9`
Input capacity	Up to 10 characters.	Up to 20 digits and then packed into 10 bytes.
Encoding logic	Each character is converted directly to its 1-byte ASCII value.	Every two digits are compressed into a single byte.

Sample custom data

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// ASCII Mode example: Encode "123abc" as ASCII bytes
byte[] asciiData = "123abc".getBytes(StandardCharsets.US_ASCII);
// Result: {0x31, 0x32, 0x33, 0x61, 0x62, 0x63}

// BCD Mode example: Encode "12345678901234567890" as packed BCD
byte[] bcdData = new byte[]{0x12, 0x34, 0x56, 0x78, (byte)0x90,
                            0x12, 0x34, 0x56, 0x78, (byte)0x90};