Phones with caller ID on the Z80 processor, have a serious drawback: with a sharp surges, impulse noise in the mains supply fails in the work of the processor. On pages of our magazine has already commented about this issue, for example, in the article by A. Bogdanov "Revision caller ID on the Z80" ("Radio", 1996, No. 5, pp. 51). This article describes another variant of such devices.
The failure of the processor often leads not only to loss of information, which stored in the memory Aona. The phone can "pick up" or close the key set rooms. This can result in the caller is disconnected from the PBX.
To eliminate the drawback in question, we developed a device automatic reset of the processor (see figure). Its working principle is based on that fails the processor stops regenerating the display (as seen by the eight" or other mark in one of the indicator bits) and pin 1 of circuit KR580VV55 missing pulses. Their absence is a signal to reset the processor.
In operation, the pulses from the output 1 of circuit KR580VV55 is input to the logic element DD1.4. The capacitor C2 is discharged periodically through the diode VD2 and the output element DD1.4. At pin 8 of the element DD1.3 at this low level, and the signal from the generator passes to the output DD1.3.
When a failure occurs in the work Aona at pin 1 of circuit KR580VV55 constantly there is a low level. The output element DD1.4 the high level, the capacitor C2 is charged and the pulses from the generator flows through the element D01.3 on the reset input of the processor. The generator performed on the elements of DD1.1 and DD1.2. Chain VD1R2 ensures generation of pulses with a large duty cycle.
The device is assembled on a small printed circuit Board that can be placed on any free space in the body of the phone. The power of the device comes from Aona. On the motherboard Aona must cut the track, going to the output 26 of the processor, and connect to this pin to the output device.
The DD1 chip can be replaced by CLA, CLA, Diodes VD1, VD2-any low-power. Collected from the healthy parts, the device does not require the establishment.
Author: A. Zhulii, art Block, Karachay-Cherkess Republic