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Read-only memory devices in integrated design (IC ROM), which are just getting a residence permit in amateur radio practice, can significantly simplify the designed equipment, and often expand its capabilities. On the basis of ROM, various software control and monitoring devices, separate functional units of digital devices, etc. can be created.

The simplest are ROM ICs that cannot be reprogrammed, i.e., having written information to them once, it is no longer possible, as a rule, to change it in any way. These microcircuits are delivered "clean" - only zeros are written in them. When programming, the consumer into the desired words and digits by burning the appropriate jumpers in the internal ROM encryption matrix. writes units.

More often than others, the K155REZ chip is used as a "memory", which is a storage device for 32 eight-bit words. Its functional diagram is shown in fig. 1. It consists of an output address decoder D1, a 32x8 bit matrix D2 and an open-collector output buffer stage D3, which allows reading information from the ROM if there is an enable signal at the input of the inverter D4.

Fig.1. Chip K155RES.

The advantage of the K155REZ ROM is that when the power is turned off, the information recorded in it is stored for an arbitrarily long time, and also that by combining the corresponding address inputs of several microcircuits, it is possible to increase the capacity of the "memory".

On fig. Figure 2 shows a diagram of a simple "fox" code generator based on the K155REZ ROM, which allows you to generate eight different code packages.

Fig.2. Scheme of a simple "fox" code generator

The length of the code message is limited in this case to 32 clock intervals, one "dot" long, which is enough to generate the code of the first three "foxes" with all the necessary time intervals between "dashes", "dots" and signs. The code of the corresponding "fox" is selected by the switch S1. On fig. 3 shows the timing diagram of the output signal of the ROM during the formation of the signals "MOE" and "MOS".

Fig.3. ROM output diagram

To program the ROM, a table is preliminarily compiled, in which for each word the necessary state of each bit of "memory" is indicated. A programming table is given as an example in the text. to form the "fox" code. It clearly shows how the corresponding code packages are formed at the outputs of the ROM. By changing the clock frequency, the transmission rate can be adjusted.

Table 1

Note. Output program Q1 - code "MY", Q2 - "MY", Q3 - "MOS".

In some cases, there is no need to form several words, but on the contrary, it is necessary to obtain one "long" multi-bit word, for example, the codes "MOX", "M05", general call signals or the call sign of the radio station. For this, multiplexing of the ROM outputs is used (see Fig. four).

Fig.4. Multiplexing ROM outputs.

With this construction of the node, 32 characters are first displayed from the first digit of the ROM, then the device automatically switches to output information from the second digit, and so on up to the eighth, while the "Depth" of the output word increases to 256 bits.

A similar node can be used in the "telegraph key" with "memory" described in "Radio" No. 8, 1980. It will greatly simplify the key constructively.

Based on the described examples, it is possible to develop a number of digital and software devices for various purposes, which are characterized by simplicity and small dimensions.

rom program on special installations of semi-automatic and automatic types, in which a previously corrected recording program is transferred to "memory". In amateur conditions, when there is no need to program a large number of microcircuits, a manual type installation is most suitable, the diagram of which is shown in Fig. 5.

Fig.5. ROM programmer (click to enlarge)

Programming is carried out sequentially for each word and digit. The word address is set with switches SI-S5, and the bit selection is S7. On elements D1.1 and D1.2, a generator of single rectangular pulses with a duration of 50 ... 100 ms is assembled. According to the programming instructions, a single programming pulse with an amplitude of 10 ... 12,5 V must be applied to the output of the programmable discharge and to the power output, shunted by a capacitor with a capacity of 10 ... 15 microfarads. The duration of the pulse front should not exceed 1 µs. To meet this requirement, an amplifier based on transistors V6-V9 with a filter on capacitor C4 was introduced into the device. The pulse arrives at the output of the programmable discharge through the resistor R8 and the diode V2, and at the power output through the diode V5. On the elements V1, V3, R7, a programming control unit is made. If the V3 LED is off, then this indicates that there is no information written in the corresponding ROM cell.

When you press the S6 button, level 1.2 appears at the output of element D1, allowing writing to the ROM. The generated programming pulse is fed to the ROM from the emitter of the transistor V6. The recording is controlled after the button S6 is released. If the write fails, increase the voltage U2 in steps of approximately 0,5 V to a level of no more than 14 V, each time attempting to program. It should be noted that according to the technical specifications for the K155REZ IC, the programmability coefficient is at least 30% of the total number of ICs, that is, only every third microcircuit is guaranteed to be programmed.

After programming the K155REZ ROM, it must be kept at a temperature of 100 ° C for a day.

In amateur conditions, the fitness factor can be significantly increased, since in a number of cases there is an excess of free words and bits that can be switched to when the pre-selected ones are not programmable.

Author: A. Puzakov (UB5MOU), Kommunarsk; Publication: N. Bolshakov, rf.atnn.ru

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