Device for automatic reset of the processor in AON. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Telephony
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Phones with caller ID on the Z80 processor have a serious drawback: during sudden voltage surges, impulse noise in the mains, the processor fails. This problem has already been discussed on the pages of our magazine, for example, in A. Bogdanov's article "Revision of Caller ID on Z80" ("Radio", 1996, No. 5, p. 51). In this article, another variant of such a device is considered.
A processor failure often leads not only to the loss of information that was stored in the AON memory. The phone may "pick up" or close the dial key. As a result, it is possible to disconnect the subscriber from the PBX.
To eliminate the shortcoming in question, an automatic processor reset device was developed (see figure). The principle of its operation is based on the fact that in the event of a failure, the processor stops regenerating the display (this can be seen from the "eight" or other sign that appears in one of the digits of the indicator) and pulses disappear at pin 1 of the KR580BB55 chip. Their absence serves as a signal to reset the processor.
In the operating mode, the pulses from pin 1 of the KR580BB55 microcircuit are fed to the input of the logic element DD1.4. Capacitor C2 is periodically discharged through the diode VD2 and the output of the element DD1.4. At pin 8 of the DD1.3 element, the level is low, and the signal from the generator does not pass to the output of DD1.3.
In the event of a malfunction in the AON, a low level is constantly present at pin 1 of the KR580BB55 microcircuit. At the output of element DD1.4, the level is high, capacitor C2 is charged and pulses from the generator are fed through element D01.3 to the reset input of the processor. The generator is made on the elements DD1.1 and DD1.2. The VD1R2 circuit provides the formation of pulses with a large duty cycle.
The device is assembled on a small printed circuit board, which can be placed in any free space in the telephone body. The device is powered by AON. On the AON board itself, it is necessary to cut the track leading to pin 26 of the processor and connect the output of the device to this pin.
Chip DD1 can be replaced by K561LA7, K564LA7, Diodes VD1, VD2 - any low-power. Assembled from serviceable parts, the adjustment device does not require.
Author: A. Zhuliy, st. Pregradim, Karachay-Cherkess Republic
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