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Recent content by Dwight Elvey

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    Intel 8085 question

    I should clarify, I wasn't talking about early x86. Things were so much simpler then. Now we have speculative execution, register reassignment,various cache memories, multiple threads. and other tricks. Now it is fast but predicting how fast is not even possible. The same piece of code may take...
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    Intel 8085 question

    I've not looked at the SDK85 code yet but there are times when knowing the cycles counts. In the 4004 code I've worked with, there a number of code timing loops. If the system is interrupt driven, cycle counting isn't as important for simulation of working code but can make or break new code...
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    Intel 8085 question

    This brings up the question of what a simulator is. The execution of code that a processor does is not a system. The SDK-85 is a system. A simulator that simulates a SDK-85 is no longer a 8085 simulator. I've always called the distinction as instrumenting the simulator to simulate a system. A...
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    Debugging a KIM-1 computer

    I was digging through my piles of stuff for the KIM-1. I found a box of stuff marked "KIM-1 project". In it I found 6ea first pass diagnostic boards. They were functional but had two things wrong with them. I didn't mask the edge connector pins, on the bottom, so they all have solder mask on...
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    Debugging a KIM-1 computer

    As I recall, the -003 chip is only used for cassette I/O and expansion I/O. It is unlikely the source of your problems. Of course, there is the possibility of loading something on the bus but in general a lot would fail if the -003 chip was causing such problems. Pulling these chips off the...
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    Where to start with this home made system?

    You should also dump the EPROM and disassemble it. It might give some hints as to how it was setup. As was noted earlier, some pictures of the boards may help figuring things out. Although, I've done it in the past, bootstrapping a system from ground zero is difficult, it is not an impossible...
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    Any one have a BASIC interpreter written in C ?

    Hi Scott I tried to send an email from the address you posted on your home page and it bounced. Dwight
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    Any one have a BASIC interpreter written in C ?

    Someplace on the web is a copy of the PTB that I had for my Poly8080. It had a unique feature that was to add Basic instructions to the command interpreter. I don't recall if the original PTB had that feature. I added two instructions that I'd load by tape to do PEEK() and POKE(,). With that I...
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    Any one have a BASIC interpreter written in C ?

    I assume if you have C working, you are working with the split memory, like the M20 has. It has split places for data and instruction memory. I was curious as to how you implemented it? Dwight
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    IMSAI 8080 front panel intermittently has stuck bit.

    Oops, I see you found a bad switch. It is not the most common failure but it looks like it solved your problem. There are open collector drivers that drive the bus. When these fail they often fail to pull the address line low. I forget which ones but a quick peak at the schematic will tell you...
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    North Star Horizon reset switch

    Reset is a grounding switch. 3.5 ohms is enough for most TTL. Dwight
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    New England Want to buy Basic/APL IBM 5100

    Before you attempt to play this in any machine, note that the tension band is broken. The tape will not drive this way. These can be replaced. Dwight
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    North Star Horizon reset switch

    Try flipping it back and forth a number of times. It is likely that the grease inside is a little old and dry. It is better to keep it original. Dwight
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    North Star Horizon power

    I'm with Dave. 330 ohm resistors never ever go to 0.4 ohms. You have a short someplace, maybe under the resistor but it is not the resistor's fault. It is physically not possible for a 330 ohm carbon comp resistor to go down in value more than about 30%. They can go open or just some higher...
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    North Star Horizon power

    I'd start splitting things in the middle. The 78L12 is most likely thing to be easy to remove. If possible, just remove the output lead first if that doesn't get rid of the short, remove it entirely. If it does remove the short, next in line are the 1488 and 1489. ( easy to find parts, Anchor...
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