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The principle of telephone cards

There are two main types of chip telephone cards: 8 contact and 6 contact, usually 5 contacts are used in 6 contact cards, among 8 contact cards there are also instances in which only 5 contacts are used, the rest are used. Cards contain an electrically programmable ROM with a capacity of 256 * 1 bit with serial bitwise output of information and an internal incremental address counter. The write operation changes the state of the memory cells "one way", the reverse change (deletion) by the card interface is not provided. Connecting cards to a computer for reading and writing is mainly done through the LPT port. Unfortunately, many cards cannot be rewritten because after the first recording, a fuse is blown. Need to collect a phone card emulator.

The order of actions performed by the potato when making a call.

  1. Power on

  2. Reset

  3. Reading the first 8 bytes and determining whether the card is valid in this region, storing them in RAM (if necessary, with decoding).

  4. Read five bytes of units and store in RAM. Checking the conformity of the available units of card capacity encoded in the first 8 bytes.

  5. Power off

After receiving the response signal of the called party:

  1. Power on

  2. Calculating the address of the last bit not written off. (approximately 1-3 seconds after pressing the answer key)

  3. Reset

  4. The supply of the number of imp. CLK to the corresponding address of the last bit not written off.

  5. Submission of the WRITE command.

  6. Submission of the W \ C command.

  7. Reading the first 8 bytes and determining whether the card is valid in this region, storing them in RAM (if necessary, with decoding).

  8. Read five bytes of units and store in RAM. Checking the correspondence of the available units of card capacity encoded in the first 8 bytes, checking whether the units have decreased compared to the previous reading.

Power off

After a minute, if the connection is not disconnected, then steps one through nine are repeated cyclically.