Electronic key K1233KT2. Reference data

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Electronic key K1233KT2. Reference data

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The K1233KT2 electronic code key is a miniature non-volatile carrier of a unique 28-bit code. The microcircuit is designed to work in access control systems (ACS) of a contact type. On its basis, it is possible to manufacture plastic cards, key fobs, bracelets, keys to electronic locks with an individual code number.

The microcircuit can be used to identify tools, work in progress and their inventory in automated production process control systems.

In terms of functionality, the K1233KT2 microcircuit should be considered a cheap alternative to the popular DS1990A key from Dallas Semiconductor [1; 2], which is widely used in modern intercoms and locking devices, although it differs both in the code formation protocol and in the number of code combinations. The programming of the key (introduction of an individual code) is carried out in the process of its manufacture.

Chips are produced in miniature plastic cases KT-26 (TO-92) - for conventional mounting - K1233KT2P (Fig. 1, a), HKT-47 (SOT-89) - for surface - K1233KT2T (Fig. 1, b).

Electronic key K1233KT2

Key pinout: 1 - input; 2 - case (not used); 3 - common wire. In a typical connection, pin 2 remains free, but can be connected to pin 3. Connecting pins 1 and 2 can lead to key failure.

Main technical characteristics*

Consumed current, mA, at a low level signal, not less than.....0,6
no more ..... 2,2
Current consumption, mA, at a low level signal and a temperature of 25±10 °С, not less than.....0,8
no more ..... 2
The difference in current consumption, mA, with a high and low signal, not less than ..... 0,5
no more ..... 3,3
Difference of current consumption, mA, at a signal of high and low levels and a temperature of 25 ± 10 ° C, not less than..... 0,8
no more ..... 3
Transmission period of one bit, Тp1 µs, not less than.....50
no more ..... 230
Transmission period of one bit, µs, at a temperature of 25±10°C, not less than.....80
no more ..... 200
Low-level pulse duration, no more than ..... 0,4Tp1
High-level pulse duration, not less than ..... 0,6Tp1

* At a supply voltage of 1,4 V and a temperature of -40 ... +85 ° C, unless it is specifically indicated.

Limit values

The highest input DC voltage, V 3
The largest input constant negative voltage, V 0,8
Maximum current consumption .... mA 15
Ambient temperature operating range, °С -40...+85
The highest voltage of static electricity, V 4000

On fig. 2 shows the dependences of the consumed current at high 1 and low 2 levels on the constant input voltage, and in fig. 3 - negative branch of the input characteristic (it is conventionally depicted in the coordinates of the first quadrant).

Electronic key K1233KT2

The block diagram of the K1233KT2 key is shown in fig. 4. The operation of the device is clocked by the pulses of the generator. The programmed individual code is stored in the encoder-multiplexer.

(click to enlarge)

From the output of the timing diagram generator, information in a serial code goes to the output transistor VT1, which is connected to terminals 1 and 1 through a resistor R3. The power and information transmission circuits are combined, which allows you to get by with just two wires to connect the key to an external node.

When the supply voltage is applied to the microcircuit, the internal generator is turned on, the zeroing unit brings the timing diagram generator to its initial state, and the code is transmitted, starting with the synchronizing bit. In accordance with the programmed code, the microcircuit changes its resistance, causing a change in the current drawn. The resistance changes abruptly, taking two discrete values.

The microcircuit reproduces the code cyclically (Fig. 5) at a rate of one bit per period Tm of the clock generator. The frame consists of a sync bit SB, a three-bit start word SS, and four eight-bit binary code words CS, each of which contains a BC parity bit.

Electronic key K1233KT2

The transmission of the clock bit is a holding of the consumed current at a high level during the whole period Tm of the clock generator, and each bit of the start and code words is the sequential holding of the consumed current first at a low level during the time Ti, and then at a high level during the time Tm-Ti . At the same time, the duration of the high level Ti1 is approximately equal to two thirds of Tm, and the duration of the low level Ti0 is one third of Tm. In other words, the duration of the levels differ by half.

The 210-digit start word contains the development sequence number (0102=7) without parity. Each code word contains XNUMX code bits and a parity bit that completes the code word to an even number of ones in the word.

Thus, one code package of 36 bits (duration - 2,9...7,2 ms depending on the frequency of the clock generator) contains 7x4=28 information bits, which corresponds to 228=268 code combinations. It is conditionally accepted that the code starts with the least significant bit. The parity complement of the binary code makes it easy to check the validity of the code read from the chip.

The use of alternating current levels for information transmission makes it possible to reduce the requirements for the contact and transient resistance of the reading circuit. The generation of code packets by the key continues as long as it is connected to the power source.

The described method of transmitting a code message leads to the need to stabilize the supply voltage. Otherwise, for example, when powered from a constant voltage source through a current-collecting resistor, the period of transmission of logical zero and one will be inconsistent, which can make synchronization and reading of the code difficult.

The scheme of the simplest unit for reading the electronic key code is shown in fig. 6.

Electronic key K1233KT2

The code package is removed from the load resistor R3 in the collector circuit of the transistor VT1. This transistor assembled a parametric voltage regulator with an exemplary source R1VD1R2. The removed code message is fed through the comparator to the decoding microcontroller. To reduce the total number of elements of the locking device, it is advisable to use a microcontroller with a built-in analog comparator.

The controller searches for a synchronizing bit in the code sequence formed by the key - it differs from all others in that it corresponds to a high level during the entire period of the internal clock generator of the key. To facilitate synchronization, the controller can remove power from the key for a short time. After power is restored, the formation of a cyclic code sequence will begin with a synchronizing bit.

Literature

Sinyutkin A. Electronic lock on keys-"tablets" iButton - Radio, 2001, No. 2, p. 31-33; No. 3, p. 30, 31.
Sinyutkin A. Overview of devices of the iButton family - Radio, 2001, No. 6, S. 49, 50.

Authors: A. Shestakov, V. Smirnov, Bryansk

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