Master in anticipation of joining pills continuously, with a periodicity generates a pulse RESET (reset). Taking this signal, the key is waiting for its completion and gives an impulse PRESENCE (presence) of a certain duration. If the signal is too long PRESENCE, the intercom system understands that this is a short closure, and remained silent. Otherwise, the master device waits for some time and gives a command to read the ROM, it's usually the family code, in this case 33H. Notice how the transfer is made zero and one. In any case, pulse "drops" on the ground, but if one is passed, then he recovers quickly (it takes about 1 microsecond). If, however, must be zero, the momentum for some time "hanging" on the ground, then back again to one.
This is to ensure that the passive device continually replenish the energy of the capacitor, and on it was food. Next intercom stand for a while and starts to generate pulses of receiving information, only 64 of the pulse (ie there takes 64 bits of information). The key must only match the correct length. If the tablet wants to transmit a zero, it holds the bus for some time at zero, if not, then just silence. Brent Nicklas has plenty of information regarding this issue. Everything else for it does intercom.
The foregoing describes the general work interphone key. Our key works on the same principle. It laid down certain information that is read by an intercom. Then the intercom system compares this information to key with her, which is embedded in the memory controller intercom. If it matches, then the door opens. In this way laid the information that displays the symbols of an empty memory intercom, as well as in almost every intercom is free memory, and verification of information missing key intercom as his own, then otkryvaemost our key accounts for about 90%. This operation performs the intercom system in 1 – 2 seconds slower than the reading of his original keys. Please note that the principle of universal key is independent of the city where you're from and intercom company that installs and maintains intercoms. A lot of people think that key to tablet is a standard intercom small magnet, which when in contact with a reader to open the door intercom. It is not so! In fact, the tablet is a hard-wired ROM key. This memory called Touch Memory. Pill "communicates" with the intercom on the bus One-wire (single-wire interface). This bus was developed by Dallas, it allows you to talk to two or more devices of a single wire. If the device is passive (as in our case), it is also transmitted on the bus and power over a single wire. In addition to the memory of the key (pill) is a 60 pF capacitor, which provides short-term power at the time of response. The master must continually generate a signal unit for charging this capacitor to the ROM in the tablet continued to eat. Rejecting all these arcane terms, we can say simply: everything you need to run the device, transmitted only by a single wire. By the way, that the 1-Wire bus has proved so successful that it held on industrial networks, including in our country.