K1839

К1839 is a microprocessor chipset developed between 1984 and 1989 at the Angstrem Research Institute by the same team that developed the 1801BMx series of CPUs. It was the first Soviet, and later the first Russian 32-bit microprocessor system. From a programmer's point of view, it was a complete replica of the VAX 11/750 Comet and included floating point arithmetic, unlike the MicroVAX microprocessors produced by DEC. The chipset included a processor, a coprocessor for integer and floating-point arithmetic, a memory controller and a bus adapter. It was fabricated in a 3 µm process. The Electronika-32 computer and a VAX-PC board were built based on this chipset, as well as the aerospace on-board digital computer SB3541 (developed by LNPOEA - OKB "Electroavtomatika", St. Petersburg). The 1839 chipset is still in production, and is used in the control systems of the GLONASS-M satellites.
The processor had external microprogram control, that is, in addition to the CPU, a separate ROM was required (1839RE1 for special equipment or any 16kW 32-bit ROM with the appropriate cycle time). However, this does not mean that the instruction set could be modified arbitrarily since the instruction decoder was included in the circuitry of the CPU.
According to posts on the FidoNet forum MO.DEC, the arithmetic coprocessor was originally released with errors, and it was not always possible to run software written for the VAX. To circumvent this, updated microprograms were released to emulate the coprocessor functions in microcode on the CPU. Bug fixed chips were introduced at the "Comtek'93" exhibition.