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Thread: RCA Microtutor first power up

  1. #1
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    Default RCA Microtutor first power up

    Got the CPU card for my Microtutor today and decided to give it a whirl.

    The binary switches seem to set the bytes correctly. And so far if I do CL with the LD switch up and then use ST to cycle through memory contents, it seems to read back what I have - although one oddity is the starting address is displayed twice -- ie. I have to hit the ST button twice to see what's in memory location 01.

    Running a program is supposed to be done by setting the LD switch 'off', and then hitting CL and ST. No dice there. I tried a few different programs but the machine does not do anything. If I hit ST a couple times after CL, it simply starts changing memory contents to whatever the switches are set to.

    I tried pulling the CPU card to see if it still behaved the same way (ie. if the CPU card is dead), but it won't let me store anything in memory. I don't know if that suggests the CPU is possibly alive... I'm open to ideas/suggestions. It could well be operator error... I remember struggling a lot with my ELF to get it to put data in address 00.
    Last edited by falter; November 27th, 2017 at 09:38 PM.

  2. #2
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    Okay, I misread the instructions about viewing memory contents. With the LD switch up, you hit CL.. this returns the counter to 00. You then hit ST to see what is in memory location 00. Then on and on. So far so good. It stores what I'm inputting no problem. But yeah, it will not run it. If I've read the instructions correctly, you just flip down LD, hit CL to return to 00, then hit ST. Nada.

  3. #3
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    I'll have to get mine out and set it up and give it a try. Are you trying the sample programs from the MPM-109 manual? If I remember right one thing that I found odd at first about the CDP1801 compared to the CDP1802 is that the execution start address is 0001 instead of 0000.

  4. #4
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    I'm going from the manual that came with it (blue cover). IIRC the first bytes of all the programs I typed started with 00.. so maybe it skips down to 01?

  5. #5
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    I got it!

    It's the instructions' fault. The very first program, they say 'LD should be down.... press CL then ST to start'. I read that as, 'set LD to down first, then hit CL, then ST'. This does *not* work. At the back of the manual where they summarize operations, you're supposed to hit CL with the LD switch *up*, *then* drop LD down and hit ST. I did the 'countdown' program, followed the latter directions to start it and it worked perfectly!

  6. #6
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    Great that you got the complete Microtutor set now and that it seems to work. Were you able to buy the CPU board directly from the seller, or did you have to win another auction listing? Hope they didn't gouge you too much for it.

  7. #7
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    Well the seller 'found' it after the auction. They wanted to auction it (which would have meant competing with CPU collectors, who tend to go insane for rare CPUs). The consignment guy in between us managed to convince him to keep the set together, so we agreed on $200. So that's $500 for all of it. I think in an open auction a Microtutor is rare enough to probably go a bit beyond that. So I think I made out okay and dodged a bullet.

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