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Vampire 600 V1: Back to Voltage Translation
Posted on Sunday, August 04 2013 @ 12:15:29 UTC by majsta

Now when we have Vampire 600 100% stable I had one question in my mind. Did I managed to design this accelerator properly first time back in 2011. and all of the problems I had were related to my poor coding techniques. Most of the problems at beginning was related to understanding how Voltage translation works. Basically CMOS to LVCMOS and vice verse. For that purpose I used ALVT devices who are not Voltage Translators they are just 5V tolerant transceivers and that was fine because FPGA was protected from higher voltage signals. All of the signals from Amiga bus to FPGA were translated to LVCMOS and FPGA was able to recognize them. But in situation when FPGA needs to send signals to Amiga bus we will need to translate LVCMOS to CMOS and ALVT devices are unable to do that. Next redesign of the board included ALVC devices capable of complete bidirectional translation, but in the same time those are dual voltage translators and having more and more voltages on one PCB can give lot of headache in design process. Few days ago I found some information's that Amiga chipset can recognize LVCMOS signals and I had to try that and in the same time to convince myself that my original design was fine, at least hardware part. So I found V1.1 of the accelerator and connect it with few wires to last version mainly testing behavior of Address bus under LVCMOS. Due to wires signals are slightly delayed and system is not stable all the time but it works. So maybe just maybe Amiga chipset can recognize LVCMOS signals and work stable? I have also sent mail to Philips NXP engineer who was earlier helping me with their products and we will see what he has to say about this. Someone may ask why I m wasting my time on this instead starting production because demand seems high for this product. One of the reasons for performing this tests was because ALVC devices are expensive and for me hard to find. On the other hand I have about 100 ALVT devices waiting to be used and I could easily get more.
UPDATE: August 6, 2013
Maybe most important information for me from start of this project. Today I just made few test to prove that Amiga chipset can recognize LVCMOS. Accelerator started just fine in 3.3V range :)

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