Master in anticipation of joining pills continuously, with some frequency generates pulse reset (reset). Taking this signal, the key is waiting for its completion and gives impetus presence (presence) of a certain duration. If the signal presence is too long, the intercom system understands that this is a short circuit, and remained silent. Otherwise, the master device waits for some time and gives a command to read the rom, usually family code, in this case 33H. Notice how the transfer is made zero and one.
In any case, the momentum "Drops" on the ground, but if you passed one, then he recovers quickly (it takes about 1 microsecond). If, however, must be zero, the momentum for some time "hanging" on the ground, then returned again to the unit. This must be to a passive device continually replenish the energy of the capacitor, and it was food. Next intercom stand for some time and begins to generate pulses of receiving information, only 64 of the pulse (ie takes 64 bits of information). The key just needs the right to match the duration. If the tablet wants to convey to zero, it holds the bus for some time at zero, but if not, then just silence. 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 lies in the memory controller intercom. If it matches, then the door opens. In this way laid the information that displays characters blank memory intercom, as well as in almost every intercom is free memory, and reconciliation information intercom misses the key as his, then otkryvaemost our key accounts for about 90%. This operation performs the intercom at the 1 – 2 seconds slower than the reading of their original keys. Please note that the principle of universal key is independent of the city where you are and the intercom firm that installs and maintains intercoms. A lot of people think that key tablet for intercom is usually small magnet, which when in contact with a reader on the intercom opens the door. It is not so! In fact, the tablet is a hard-wired rom key. This memory called Touch Memory. Pill "communicate" with intercom on the bus One-wire (single-wire interface). This bus was developed by Dallas, it allows you to communicate with two or more devices all on one wire. If the device is passive (as in our case), then the bus is also transmitted and power over a single wire. In addition to the memory in the key (pill) is a 60 pF capacitor, which provides short-term power at the time of response. The master device must continually generate a signal unit for charging the capacitor to rom in the tablet continued to eat. Dropping all these abstruse terms, we can say simply: all that is needed to operate a device, transmitted only on one wire. By the way, that the 1-Wire bus has proved so successful that it organized industrial networks, including in our country.