Java Card

Im having trouble with the values of Le and Lc. I have created a 256 byte array in my code and I am attempting to read from and write to it as two blocks of 128 bytes. However, my code goes haywire when I set either Le or Lc to 128. I found somewhere a reference to the BER-TLV standard and on reencoding my Lc to 0x81 and putting 0x80 as the first byte of my data I was able to get a result from my card - it was an error because I hadn't allowed for this in my code but at least it went through. Can someone please tell me where this is defined, because I have been using ISO7816 smartcards for 3 or 4 years now and have been passing back and forth data arrays of 128 bytes and larger on other card platforms without problem. This is my first Javacard application, so if I'm being dim please go easy on me.

Thanks,

Andrew