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(Hardware) Project of the 'calendar quarter'

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No problems there, I do a lot of layouts--and if you route the trace from pin 6 between pins 8 and 9 of the 74LS21, you don't need a bridge at all. . .depending on how wide you want it. 10 thousandths of an inch is more than enough for a signal line, so long as you keep all corners at 45 degrees instead of 90.

 

Your idea to put this onto a small board is a good one, as it will make this project a LOT easier to do.

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Coincidentally, I didn't put two-and-two together until I put the creator's name on the silk screen, Mike Brent, then it sunk in, I work with the guy who created this mod. Small world.

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Oh, RAT FARTS!

 

I've had no time to do ANY projects lately, but the ONE THING that I did do, when I managed to shoe-horn in a couple of minutes .... was to prep my 74LS21. Now it looks like I may need to buy another if this board project comes to fruition. Good thing it's a 'quarterly' project.

 

I do have a question though. Where under the 'clam shell' do you plan to attach and secure this board? Will it fit?

 

 

gallery_35324_1027_65797.jpg

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Coincidentally, I didn't put two-and-two together until I put the creator's name on the silk screen, Mike Brent, then it sunk in, I work with the guy who created this mod. Small world.

 

Ahhh, now the mystery begins! ;)

 

or I'm just tired cause it's the 5am end of a midnight shift... ;)

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Looking at the board again, it occurs to me that you could add a couple of pads and have the disable switch discussed above, too. People who don't want the switch can just wire across the pads. :) Thanks for adding a credit!

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Sounds like you've been Shanghai'd. Are the mosquitoes gone yet? When Matt updated the firmware on my F18A I just threw the 99's RF shielding into the recycling bin, as I consider it to be a worthless heat trap coated with Erin Brokovich-upsetting-hexavalent-chromium. I actually watch TV from a rooftop antenna, (so much cleaner than compressed cable) and haven't seen any interference from the TI.

 

Anyways so I didn't really think about the vertical fit. I guess I'll need to use the surrounding componenents to judge clearance, as long as we're no higher than the highest existing item we should be OK. Also hadn't yet given any thought to finding the least hot area near the potential board placement, offhand I'm guessing that somewhere near the 74 ic's is cooler than over the ram. I didn't see the switch suggestion (I don't have a NanoPeb) but the Eagle file should be easy enough to modify.

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I doubt you'll have clearance issues, piggy-backing chips on the mainboard has never been an issue, and you aren't adding much more height than that. :)

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I doubt you'll have clearance issues, piggy-backing chips on the mainboard has never been an issue, and you aren't adding much more height than that. :)

 

I think he was referring to using his PCB design with the chips on-board. There may be some placement issues under the clam-shell for those who choose go that route.

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I

I think he was referring to using his PCB design with the chips on-board. There may be some placement issues under the clam-shell for those who choose go that route.

I hope so, cause that's what I was talking about :)

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With my mod, I guess you have lots of options, but I'd probably disable it with a switch on the RAM's Chip Enable line (pin 20). One side to the AND gate as per the docs and one to +5v (optionally through a small resistor, 1k or so). When the switch is placed in the 5v selection, the chip enable is permanently high and the RAM chip will never respond. Flicking the switch while the system is running may cause a crash (less likely if not using the 32k at the time, but it is always possible).

 

With a pull-up resistor you can use an SPST switch on the same line -- the pull up resistor goes from CE to any +5V source, and the switch is inline with the wire to the AND gate. I don't like it quite as much because the system has to override the resistor to activate the chip, and the console kind of has a lot of that going on already. You'd probably want to try a 10k resistor here, though.

 

I think I might have followed that correctly, though I'm not sure which of the two resistor values to use (I'm guessing the 1K.) I will go with this layout then:

65fa80f8995442aa337176d4c66edf1d

 

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I think I might have followed that correctly, though I'm not sure which of the two resistor values to use (I'm guessing the 1K.) I will go with this layout then:

That looks right to me. Either resistor will probably work... I think there is an actual knack to picking pull up resistor values but the 1k will drive it a little more strongly than the 10k, and since it doesn't need to be overridden, it gives me warm fuzzies. ;) Even if full current was flowing, it's only 1mA. :)

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I've ordered this revision from Osh Park, $21 for qty 3. If it works properly, I'll hit the project's "Start sharing" button on their website so that anyone can order.

 

Amazon sent a delivery estimate on the ram chip of Jan 30, so I gather that it ships from China, I'll check Burbank Electronics City in the meantime to see if I can get one faster as I'm sure I don't want to wait that long. (Edit: I just found out they're out of business.)

Edited by towmater
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Urf, I fail the Corcomp Test, which is, I believe, a modified Voight-Kampf.

As you can see it hit the 32k ram's starting address and immediately quit. I have quad-triple checked the wiring, and tested continuity on all, it looks fine. I guess I will do an identical installation on a second TI-99 and see if I get the same results, but unless I am missing something, I can't fathom what's wrong.

ti32k install

ti32k

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I thought a Voight-Kampff test in that context would be:

 

Q: You unpack your newly acquired TI console and attempt to add a 32K expansion inside. After finishing you switch on power and notice a strong smell and bluish clouds emitting through the chassis, later you notice you swapped some lines. How do you feel?

 

A: I shrug and try to do better next time.

 

-> Replicant

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OK, phew, it's a good thing Osh Park makes you order three boards minimum, my second attempt at this seemed to go without a hitch. The main difference this time is that I used 22-gauge solid wire instead of braided ide hard drive wires. If I don't see any crashes or hiccups in the next few hours after I put the case together, I'll post a link to the Osh Park project page if anyone wants to do it themselves. Their prices were pretty reasonable and delivery was only a week or so.

ti ram working

Edited by towmater
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It's good! All credit to Tursi. If you want to order, search on Osh Park for:

"TI/99-4A 32 Ram rev 2"

 

 

Sorry, flubbed that. Search for "Ti-99/4A 32K Ram rev 2"

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The SAMS memory upgrade puts 1Meg of memory into a TI and is very dinky in size.

With newer chips why not put 1Meg into a TI99 instead of just 32K?

 

The cost benefit of just 32K vs 1Meg pretty much makes it look like a silly project to do.

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