java - How can i credit or debit more than 1 byte to/from card?

Question

I am newbie applets and i used from this link: working with Java Card Wallet for creating an Wallet project. I before could credit card amount by this command : 80 30 00 00 01 1A 00.

I now want add '5000' to the present amount. As you know 5000 in hex equals

with '1388' that is 2 byte. So i must send 2 byte data 13 and 88 to the card.

I create bellow command and sent it to card but i get '67 00 Wrong lenght' as

response.

80 30 00 00 02 13 88 00

How can i credit or debit more than 1 byte to/from card?

Answer 1

You'll have to change the code of the Applet you're pointing to of course:

if ((numBytes != 1) || (byteRead != 1)) {
    ISOException.throwIt(ISO7816.SW_WRONG_LENGTH); // constant with value 0x6700
}

So you must make sure that it allows for 2 bytes to be send, then you can use the Util.getShort method to convert to the bytes to a 16 bit signed value (using big endian two complement notation, as usual).