The principle of operation of telephone cards. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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The principle of operation of telephone cards. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Telephony

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There are two main types of chip telephone cards, these are 8-pin and 6-pin, usually 6 contacts are used in 5 contact cards, among 8 contact cards there are also instances in which only 5 contacts are also used, the rest are loaded.

The cards contain an electrically programmable ROM with a capacity of 256 * 1 bits with serial bit-by-bit output of information and an internal incremental address counter. The write operation changes the state of the memory cells "in one direction", the reverse change (erasing) is not provided by the card interface.

Connecting cards to a computer for reading and writing is mainly carried out through the LPT port. Unfortunately, the cards cannot be rewritten because the fuse is blown after the first recording. You need to build a phone card emulator.

The order of actions performed by the card phone when calling

Power on.
Reset.
Reading the first 8 bytes and determining whether the card is valid in the given region, storing them in RAM (with decoding if necessary).
Read five bytes of ones and store in RAM. Checking if the available capacity units of the card encoded in the first 8 bytes match.
Power off.

After receiving the dial tone of the called party

Power on.
Calculation of the address of the last unwritten bit. (approximately 1-3 seconds after pressing the "answer" key)
Reset.
Feeding the number of imp. CLK to the corresponding address of the last unwritten bit.
Issuing the WRITE command.
Issuing a WC command.
Reading the first 8 bytes and determining whether the card is valid in the given region, storing them in RAM (with decoding if necessary).
Read five bytes of ones and store in RAM. Checking if the available capacity units of the card encoded in the first 8 bytes match, checking if the units have decreased compared to the previous read.

Power off.

After a minute, if the connection is not broken, then the steps from the first to the ninth are repeated cyclically.

Publication: pozitron.ru, radioradar.net

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