Questions tagged [pdp-11]

For questions regarding the DEC PDP-11 minicomputer.

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12 votes
1 answer

Can PDP-11 general registers be referenced by memory addresses?

From time to time it is mentioned in RC that the PDP-11 general registers R0-R7 are accessible at addresses 177700 to 177717 (considered as 16 bit program addresses). The mapping is as follows, again ...
another-dave's user avatar
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2 votes
3 answers

PDP-11 JMP and JSR - how was the target specified?

As I understand it, the PDP-11 has a 16-bit address space with a fully loaded system having 28k words (56k bytes) after reserving some of the address space for I/O, which means if instructions must be ...
rwallace's user avatar
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57 votes
8 answers

How were Western computer chips reverse-engineered in USSR?

The British ZX Spectrum computer had many clones in the Eastern Bloc. It seems many of them were built using Russian-made chips from the Angstrem factory in Zelenograd in/near Moscow. The Russian ...
Omar and Lorraine's user avatar
50 votes
3 answers

Why did the PDP-11 include a JMP instruction?

The PDP-11's program counter was addressable in two ways: as a general purpose register or as a memory location. Still, the PDP-11's instruction set included separate instructions for moving a new ...
Omar and Lorraine's user avatar
23 votes
5 answers

Were there any LSI-11 like home computers outside of Russia?

In my childhood I had one of these: Note, that the CPU of this is based on LSI-11. This is rather surprising because PDP-11 took a room (I was lucky ...
Andrew Savinykh's user avatar
22 votes
4 answers

PDP-11 instruction set inconsistencies

The wiki page PDP-11 architecture has a cryptic paragraph with no references or examples: Inconsistent instructions Over the life of the PDP-11, subtle differences arose in the implementation of ...
Leo B.'s user avatar
  • 18.3k
6 votes
1 answer

'Trap stack push abort' on the PDP-11 with SIMH

I'm trying to run a bare-metal example program from the DL11 manual that echoes user input. When I try to run it via SIMH however I get a 'Trap stack push abort' error when it tries to access address ...
DivergentClouds's user avatar