In the Soviet Union, Z80 compatibles were manufactured under at least the following designations:

  • Т34ВМ1
  • КМ1858ВМ1
  • КР1858ВМ3

At least some of these were manufactured from the U880 masks that were developed in VEB Mikroelektronik, in the German Democratic Republic, as evidenced by the markings on the die. But why were all these three designations in use? Weren't they actually the same part exactly? Or was there some kind of hardware difference (maximum clock speed, voltage levels, whatever) or software difference (new instructions, bugfixes)?

  • 1
    "developed" is maybe not the proper term. And the GDR preferred to leave out the quotes.
    – tofro
    Commented Jun 18, 2019 at 11:34
  • 4
    @tofro You're right, I'll remove the quotes. But why is "developed" not the right term? AFAIK it was blackbox reverse engineered? Commented Jun 18, 2019 at 11:47

2 Answers 2

  • КР1858ВМ3 used 2μm lithography unlike the earlier variants using 4μm lithography.
  • Т34ВМ1 and КР1858ВМ1 were both based on U880 masks, while for КР1858ВМ3 the manufacturer seems to have designed an original topology. The irony is, КР1858ВМ3 had a larger physical chip size despite 2μm lithography.
  • Т34ВМ1 was considered as experimental series produced exclusively by the "Angstrem" factory. КР1858ВМ1 was a natural evolution of the T34BM1 series that was produced by a number of manufacturers in ex-USSR.
  • Rumor also has it that КР1858ВМ3 also featured lower energy consumption as it was intended rather for battery-powered embedded systems than for ZX Spectrum clones.
  • On some accounts, КР1858ВМ3 was almost a complete clone of Z80A (Z84C004), with the only difference in internal processing of the HALT command (unlike the original, КР1858ВМ3 does not wait for completion of the current "idle cycle" NOP command while waiting for an interrupt).
  • Unlike КР1858ВМ1, КР1858ВМ3 was produced only by the Belarussian factory named "Transistor", and the production started only circa 1995-1996.

At least, KP1858BM1 and KP1858BM3 are completely different designs, starting from the fact that BM1 is NMOS and BM3 is CMOS.

Also it is known that BM3 differs in execution of HALT command: while the original Z80, whether it is NMOS or CMOS, makes idle M1 opcode fetches during HALT (thus supporting DRAM refresh), BM3 simply ceases all activity. As the consequence, Z80 exits HALT state with the granularity of 4 clocks, while BM3 exits immediately.

According to these two links: http://www.155la3.ru/t34vm1.htm and http://www.155la3.ru/k1858.htm, both T34BM1 and KP1858BM1 first were the clones of U880 design (or simply used the original dies of U880 from DDR) and then switched to differing (self-made?) design. U880 die has a clear writing of "U880/5" or "U880/6" on the edge, while the newer design has a heart symbol in the middle of the die.

According to this https://gist.github.com/drhelius/8497817, there are also some important differences in undocumented behavior between the original NMOS Z80 and T34BM1/KP1858BM1, while it seems that the authors did not try to distinguish U880 dies from later original KP1858BM1 dies, nor they specifically tested original U880s.

  • 3
    Not sure if a typo or not: You got KP1858BM1 but I had КМ1858ВМ1. Does this part of the designation specify NMOS or CMOS? Commented Jun 18, 2019 at 12:50
  • 4
    This specifies only the package. KP might be a plastic DIP, while KM might be ceramic DIP.
    – lvd
    Commented Jun 18, 2019 at 14:55

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