Hi Roger, thank you for your detailed information. By accident I nearly missed your email since I was not listed to the cctalk mailing list. But this is solved now ;-) I will comment some points of your email now and hopefully I will find the time next week to investigate your other suggestions and hints on the machine. I will give an update next weekend. OK, I understand this. I do not know much about these issues, but on the internet often the COTS strategy is mentioned and in using standard components, I think moderen aircraft swap technology more often than was done in the 60s and 70s, right? Thank you - I will try to find information on the web in the next days. Compared to the Elliott machines the DECs are very common stuff ;-) Thank you for this hint. I checked wikipedia and obviously GEC got involved very early and the name was changed to GEC later (1984). Sorry for my misunderstanding, now I got it. The internet claimes sometimes, that core memory is less sensitive to radiation, too. This might have been an advantage in certain military applications (really bad applications, honestly speaking). Data retenttion of the core memory should be quite good, but since reading is always destructive, there is the rist, that bad data gets written back. In the case of Programmer Electronic Control, they did quite a lot to adjust the core memory's dirver current automatically according to a temerature measurement of the core. As my experiments show, you have to reduce the current if temperatuere goes up. This physically understandable (1/T). Hey, that is even better. I highly appreciate, that you spend time in sharing your information! Thanks a lot in advance! In my case they are relative and you can jump +/-127 words (crossing any border). Here again, the box uses 1complement and thus jump 0x00 is the same as jump 0x80: An infinite loop! Hmm, I do not understand fully what you mean by "the following instruction was either an 8 or a "/8", i.e. 24". The Programmer Electronic Control (Let's call it PEC in the future) stores PC+1 (as your 18bit) to the specified location into core. The new address is taken from the position in memory where the index register points to. So in my case this is a perfect table jump. Results are as you mention, but if either operand is negative, the result contains wrong values. But maybe I check whether this depends on the content of the index register prior to the operation... OK, I will verify this in the coming days. Now I know what to look form but according to my records the results of this command always have been junk. Right. But here again, the bit 11 is the sign bit and thus the shift does not affect the bit 11 of the destination. I.e. bit 0 of A is moved to bit 10 of Q in shifting right for example. Yes, the load immediate is really nice. A block move does not exist on PEC. Essentially the immediate "MTA - Move To Accu" is one of two "two-read-cycles" instructions. Up to now I did not fugire out, what the other instruction does with the data read. Do you remember any "two-read" instructions in the Elliotts? Yes, this seems to be absolutely correct! Correct: Everything is modified by the index register. Exceptions are the jumps, MTA for example. You are clever - that is exactly what appens: Every instruction which is affected by this register (ADD, SUB, LDA, STA, ...) clear the register. So you have to load it right before each instruction. A severe constraint in my opinion is, that the index register can only be loaded from words 0-127 in the lower 4k. So this might be a bottleneck in memory since the table jump (I called it IDXCALL since it used the index register to get ne new address from) requires memory for each routine called, too. Great! T H A N K S a L O T! Thanks - is stored into my brain now ;-) No, if the machine is held in reset state, the PC is forced to 0x0a0 since the reset line is connected to the Set/Clear pins of the flip-flops making the program counter. Immediately after reset is set high, the first word is read and executed Some kind of blinking-light console? Something like this exists for the Rolm 1666b, too. This would be cool to have! ;-) If data gets corrupted, than the complete aircraft has to return to a maintenance depot for reprogramming the machine? So if there are 10 or 20 of these boxes in one aircraft, they need service quite often I think. Roger, how was your experience - was this reliable with the Elliotts or did you have to reporgram the pater tape loader quite often? In my case, the transputer setup generates some spikes doring it bootup. If PEC is already turned on, this corrupts the data in core memory. So I always do a memory-test on PEC after turn on (to adjust the core driver current) and than freshly program my test routines. So 15 7168 increases the interrupt level and after executing this once, the interrupt 1 can be serviced, right? What happens in the Elliott, if an interrupt occurs? Is there a jump to a certain address in core or is the new program counter itself read from core? I have to think how to figure this out for PEC.... Of course I have to apply signals to all possible interrupt sources, load a program trying the yet unknown instructions and watch wheter any irregularities or jumps occur. I will have to trap PEC if the idle-loop is left. This is a bigger project and I will need some weeks to check this. Thank you very much for this list. This gives me valuable hints and ideas what to try out next. BTW: Have there been timers on the Elliotts you know about? Since you are such an expert I am sure you have a nice collection of vintage hardware, right? Perhaps you even have got an Elliott up and running? Thanks again, best regards, Erik.