We first went to a site http://www.compt.ru/serial-port-monitor/en/download.php from where we downloaded the program that lets us send some bytes to a com port. When we start this program we see two windows, the one on the left is data that we send to the com port and the one on the right is the data received from the com port. Any program that allows us to send bytes to a com port could be used. We have a sim card reader that connects to a USB port but we have installed a driver from a company A-Men that lets this usb port look like a com port. In our case it is com port 3. In the toolbar the fifth icon is com port configuration. We click here and change the com port to 3, the baud rate to 9600, data bits to 8, Parity to even, stop bits to 2 and finally flow control to No. These are the settings that the sim card reader wants from us if we have to communicate with it.

To test whether things are working we send the some bytes to the sim card and check whether we get the right answer. We click on the menu message and then send. In the first text box we write the bytes a0 a4 00 00 02. When we click on send we get the following bytes in the second window pane - A0 A4 00 00 02 A4. Thus the sim card simply repeats whatever bytes we send it. It adds an extra character, the command number a4 which is command select. The number 2 at the end is that we will send you two bytes in the next round. The two zeroes are extra parameters that we will discuss later. Thus a sim command starts with a0 always, followed by the command, some extra parameters and the length of the next bytes. The sim card replies with the same bytes we have send and the command number. We then send the two bytes which is the name of the first file/directory. This is 3f 00. When we send these bytes we get another answer, 3f 00 9f 19. Thus our bytes get echoed, then a success or failure code 9f means ok and then the number of bytes the system has to send us. We now need a command to fetch these bytes for us. Thus we send the bytes a0 c0 00 00 19. c0 is the command to fetch bytes for us and the last number 19 is the number of bytes we need. The system now responds as A0 C0 00 00 19 C0 00 00 00 6A 3F 00 01 01 00 FF FF 01 0C 91 04 0B 06 00 82 89 82 8A 00 80 83 90 00. The first bytes are always what we have send the sim card, then the 19 hex bytes the sim card has send us.