U1MB Installation Challenges - 800XL

[Piotr D. Kaczorowski]

1 hour ago, TZJB said:

@Dr Memory, regarding U18, as you point out it does buffer Phi2. For this reason many people exchange that component for a 74F08 when installing a U1MB to prevent timing issues, I seem to remember.

The BO2 (Buffered O2 => Buffered Phase 2) clock path is often heavily burdened by various devices. Additionally, there are indeed timing issues because people connect the Ultimate 1MB to the O2 line instead of the BO2. Even if you purchase the SRAM 64K V3, there is an O2 connector for the Ultimate 1MB that shouldn't be there, because as I mentioned, every circuit inside and outside the Atari should be connected to BO2. One way to increase the stability of the Atari is to replace the 74LS08 chip (in some Atari computers, this is 74HCT08 - e.g., Atari XEGS) with the 74F08 chip. The 74F08 chip belongs to the F.A.S.T. (Fairchild Advanced Schottky TTL) family, which is designed to operate up to 125MHz, achieved by minimizing the increase in parasitic capacitance on the connections to which it is attached.

 

If you want even better quality, you can use the O2/Fixer, which is an implementation of two 7408 chips based on the 1-gate AHCT, which operate at speeds above 1GHz (the original O2/Fixer is simply 2x 74F08 on one board). The O2/Fixer has 8 AND gates, 7 of which have NMOS characteristics, and one has CMOS characteristics (strong rectangular signal), which is dedicated to the Ultimate 1MB and other circuits designed based on CMOS components. Personally, I have very good experiences with these systems. Currently, I have six Atari computers with Rapidus extensions in service, and all of them work stably using the O2/Fixer. In Poland, the O2/Fixer costs about 7 EUR. In my opinion, it should be included for free with U1MB and SIDE3, but that's not my decision.

[Piotr D. Kaczorowski]

1 hour ago, TZJB said:

I have never needed to replace U18 with a 74F08 though, as I use AVGCART 😉!

SIDE 3.0 and 3.1 are designed using Lattice FPGA, while SIDE 3.2 is designed using GoWIN FPGA.

 

AVGCART is designed using the Efinix Trion T20 FPGA.

 

In my opinion, the Trion T20 is the more advanced option. AVGCart's construction is less complex, and TMP handles both the hardware and software. That's why AVG is a very stable solution.

 

But... in fact, I use SIDE 3.1 because it was a challenge to make it work, and I love FJC's software on it. In my opinion, SIDE 3.1 combined with Ultimate 1MB is more advanced than AVG.

[+mytek]

On 3/6/2021 at 7:39 AM, Dr Memory said:

You are correct that you show the vias in your video, briefly

I read this and got a chuckle. You do realize that you can pause and step through any video? Saying briefly makes it seem like you were unaware of being able to do that.

 

However I do realize that this can seem daunting the first time you open the U1MB box and see all the cables, and without a prior build under your belt, it will certainly take time if you're trying to be careful and not make a mistake. My very first time I put it off for about 3 days, until I was well rested and in a good mood

 

And lastly Lotharek isn't known for having good installation docs, so you are ever so better off seeing if @flashjazzcat either has something on his website, or has done a video on your particular computer model installation. In fact he's probably installed every piece of upgrade hardware ever made for the Atari.