SIMH LGP-30 Progress.

B Degnan billdeg at
Wed Feb 11 12:23:42 CST 2015

On Wed, 11 Feb 2015, B Degnan wrote:
> > via trial and error, and a lot of reading.  I believe that loading the
> > bootstrap manually is a must; one cannot use or create tapes 
> Only if your drum memory loses its contents. I don't know if SIMH has a 
> concept of non-volatile main storage (drum, core). And for the LGP-30, 
> registers are non-volatile, too.

When I fire up the SIMH and check 6300 we have 


If the bootstrap came pre-loaded the first instruction of bootstrap should 
be in 6300 and read 


so, no unless the bootstrap is somewhere other than where I think it should 
be, memory is completely blank when SIMH is loaded. 

> > In order to enter instructions into memory I first learned how to 
> > code from the various actual papertape sources, for example...
> >
> > "flexowriter entry"> 6300 P 0000'
> >
> > becomes
> >
> > sim> d -a 6300 10000000
> Urks, that's sick... but SIMH should offer the possibility to enter the 
> mnemonics and addresses (or anything else since everything is mapped to 
> its four bit code) like
> sim> d -a 3w00 p0000     (or d -a 6300 p0000 

sim> d -a 3w00 p0000 

Invalid argument  

The SIMH *should* accept mnemonics ... Believe me I tried EVERYTHING ... 
but unless there are hidden command switches you have to convert your code 
to machine format.  Scoured the entire C source code looking for clues.  

> sim> g 3w00 

g is not a legal command.  You have to tell SIMH to execute with a "SET CPU 

> Anyways, SIMH is not very well suited for machines like an LGP-30 where 
> the user interaction with typewriter and console buttons for operation is 

> imperative. The SIMH version does officially work, but it is not really 
> user friendly in this case. 

Tell me about it.  I have written to the SIMH user group, so far I have not 
received a reply with tips/testing done to verify "officially work" 

> But the best would be if you use a drum image with 10.4 (the monitor) 
> already loaded, i.e. save the memory contents to a file and reload it on 

> the next incarnation of SIMH (there's a "START" drum containing 10.4 in 
> simulator package, and an "ACT5" drum with preloaded ACT-V and 
> subroutines, these may be usable in SIMH, but I don't know).
> > repertoire.  The hardest part is finding ways to enter Flexowriter key
> > input via a modern keyboard, using SIMH commands.
> By using a simulator that offers the right frontend to the user (i.e. 
> and buttons as required by the machine operations) *g*
> Christian

Christian....I am going to keep at it and then script a bootstrap that will 
load in SIMH, or convert tapes to SIMH format so they can be imported.  I 
can see why you did what you did with your simulator.  Makes a lot of sense 
to use function keys. 

Here is the bootstrap I am working to complete. I need to find equivalents 
to the Flexowriter commands, I have finished the memory insert commands, 
please send suggestions if you have them. 

sim> [first cpu fill c6300 in IR?] 
sim> d -a 6300 10000000 
sim> d -a 6301 01000000 
sim> d -a 6302 11016305 
sim> d -a 6303 10000000 
sim> d -a 6304 01000000 

here is where I need to experiment, the code below is my first attempt: 
6305 (skip) 
6306 10106300 
6307 10000000 
6308 01000000 
6309 (skip O.G.W.C flexo keys, still need to convert) 
6310 00016346 
6311 11116326 
6312 10106322 
6313 00000000 
6314 10100000 
6322 10116313 
6323 11006309 
6324 11016346 
6325 10106307 
6326 000wwwwj (entered into by flexowr., need to convert) 
6346 0gwc0000 (entered into by flexor, need to convert)                 


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