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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...

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...

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...

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...

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...

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...

Hi Scott I tried to send an email from the address you posted on your home page and it bounced. Dwight

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...

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

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...

Reset is a grounding switch. 3.5 ohms is enough for most TTL. Dwight

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

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

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...

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...

Yes there is a short circuit. First I'd like to make sure the right regulators are on the right power rail. This was the reason I wanted the voltages seen as the regulators. There isn't that much on the supply line sides of the regulators. These regulators have output short protections that can...

Are the disk drives connected? if so disconnect them. Also, the 78L12 and 79L12 are voltage regulators. They do not have emitter, base or collector. Look for the spec, on line, for these to show what pins are input, ground and output. Also, this size transistor can have at least 2 different...

Was it an alkaline type battery? ( NoCads are alkaline) If so, first remove any flux with the alcohol. Then use white vinegar to get things clean. It might take several hours. Then rinse with water. When clean follow others soldering instructions. Dwight

I've got a suggestion. Take to low wattage 12V lamps ( find them at an automotive store ). Put them in series between the supply and the load. Don't worry about the bulbs taking 16V. They should be able to handle that for hours. Most interior lights are about 3 to 5 watt. Most dash lamps are...

I should mention that early versions EForth where intended to be easily modified and portable to other environments. It was not intended that the developers would provide patches to make it work in someone else's environment. The version of EForth that I have running on my Blue Pill was...