Smart cards follow a specific protocol when talking to the reader and/or the PC. One commonly mentioned phrase, T=0, T=1, is used to describe the protocol used to communicate to the card from the reader. T=0 is a byte oriented protocol in that every byte that is sent, an Acknowledgement must be received. With T=1, a specific length of bytes can be sent in a data block. Information is sent to the reader in hex code format. The Schlumberger Reflex 60 has the following commands:
0x60 Gets Reader Type and Activate Reader
0x61 Sets Reader with ICC communication parameters
0x62 Turns Card Power ON
0x63 Turns Card Power OFF
0x64 Sends Reset to Card
0x65 Gets Reader-Card Status
0x66 Sends one byte to Reader
0x67 Sends Data Block to Reader
0x68 Makes Reader Resend last data block
0x69 Gets Reader Capabilities
0x6A Deactivate Reader
0x6B Activate Reader-Dependent Features
0x6C-0x6F Reserved
A typical command to the card would include the reader command and also the card command. A Get Challenge command from a card would look like this:
0x67 0x00 0x05 0xC0 0x84 0x00 0x00 0x08

The first three bytes [ 0x67 0x00 0x05 ] indicate that the following command should be sent to the card. 0x05 is the size of the command that follows. [ 0xC0 0x84 0x00 0x00 0x08 ] is the actual card command for doing the Get Challenge. ISO standards set the way the commands are handled by the following command set standard:

0xC0 would be the class,[ 0x84 ] would be the instructions, and [ 0x00 0x00 0x08 ] would be the three Parameters. ([ 0x08 ] is the desired return size of the Get Challenge).