Petr
Designed by Institut mikroelektronických aplikací, Matematicko-fyzikální fakulta Univerzity Karlovy v Praze.It was manufactured from 1988 by Tesla ELTOS. Hardware is based on MHB8048 @ 6MHz.
The PETR microcomputer is a universal kit of a small control computer, which was designed primarily for polytechnic teaching. The kit is delivered in the form of individual parts that, after assembly, the user can program like a regular microcomputer. The original goal of the creators was to create a device with a simple architecture that would still be able to control real applications such as models, measuring and evaluation devices, signaling systems or track control. One of the main requirements was low cost, due to which most of the functions are implemented in software through the control program, not by hardware circuits.
The first version of the PETR kit was released on the market in 1986 and was created thanks to the cooperation of the employees of TESLA ELTOS, the Institute of Microelectronic Applications and the Faculty of Mathematics and Physics of Charles University in Prague. The inspiration for this project was the small KOSMOS microcomputer manufactured in West Germany. Although PETR has been improved functionally and structurally, and its technical solution is significantly different from KOSMOS, as a symbolic reminder of its inspiration, PETR's microcomputer displays the letter "C" when turned on.
The basis of the PETR kit is a single-chip microcomputer of the 8048 series, which operates at a frequency of 6 MHz and contains 1 KB of ROM or EPROM memory. After the initial tests, the kit was technically improved so that it could be used universally. Users can thus complement the existing circuit solution with their own control program, which means that the kit can be adapted to more demanding applications, for example heating automation or security systems for homes. Thanks to its modularity, PETR becomes not only a teaching tool, but also a suitable semi-finished product for various practical projects.
The PETR kit is designed with flexibility in mind and users can expand it with their own control program stored in external EPROM memory. The Reset signal is automatically activated when the power is turned on or manually via a button on the foil keyboard. Soldering points are also available on the base plate for connecting the stepper, but it is not part of the kit.
The mechanical construction of the PETR kit is designed so that the individual parts can be easily placed in the case originally intended for the Tesla Bratislava desktop calculator. The case consists of two parts. On the upper part there is a foil keyboard, a DIN connector for connecting a tape recorder and a switch. The lower part is modified by a cut-out in the back wall, through which the motherboard with a contact user field protrudes, which facilitates the connection of the microcomputer to external devices. Both parts of the case are connected by screws through the angles, which are inserted into the cutouts in the upper part.
The circuitry of the PETR microcomputer includes the power supply part, the microcomputer core itself, the keyboard and display circuits, as well as the interface for connecting the tape recorder. The main elements of the microcomputer are two integrated circuits, while the core of the system is a single-chip crystal-controlled microcomputer with a frequency of 6 MHz. This microcomputer contains a control monitor and a command interpreter stored in program memory. Gate P1 serves as a bidirectional bus that is output to the contact field and enables direct communication with external devices. The contact field also includes input signals T0 and INT. The T0 signal is idle at logic level 1 and can be tested from the program. The INT signal is used to enable external interrupts that occur when transitioning to logic level 0. These interrupts enable efficient handling of external events.