5V FCT TO Cyclone II

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I am assuming that you are attaching the FPGA as a memory-mapped device, which means that most of the signals will be unidirectional. For these, I would suggest a simple buffer with a wide input range. I have used the SN74LVC2G34 buffers where I need to drive a 3.3V input on an FPGA with a TTL device, and they have worked very well. Just power the buffer with the Vio of your FPGA, since the inputs are tolerant up to 5.5V regardless of Vcc. You can get devices with the same specifications in hex and octal variants.

For the bi-directional bus, I do suggest the IDT quickswitch parts. They are are cheap, have extremely small latencies, and are fairly simple to use. The only caveat is that to use them as voltage translators, you do have to pay attention to the A and B side (since they are FET based, and have an intrinsic diode), and note that you have to supply them with a Vcc no greater than 4.2V to ensure the output never exceeds 3.3V. However, the current demand is very small, and most people get away with just putting a small signal diode between the supply and the part's Vcc input. Just make sure the diode has a Vf greater than 0.8V.

Yes in my first design i used quickswich devices but then i decide to go to the newer devices like txs0108e. This is octal bi-directional bus with voltage level translation. And now i dont know is this design ok becuse like you write in previus post best metod is to use quickswich. What do you think about txs0108e in this design. Also i would not use cyclone just for memory, i want to use mc68000 core with sdram controler to replace mc68000 on the board.

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I would offer You to use simple and trivial SN74LVC8T245. Thats also 8bit translator with two voltages.

Why not stay with the switches? That saves you from switching direction in the drivers.

Bye

Make sure when you use a converter like that that Vih on the 5V side is low enough for TTL. From the looks of it, that is *not* true for TXS0108E when Vccb = 5V.

The reason quickswitches work for 5 V TTL 3.3 V CMOS is because

-hpa

Ok but i ll stay with this design, I dont know I just cant change design now, and many peolpe told me that it can work with txs0108e. Thank you for your time. Also I want to ask is there are any examples of Mc68000 and sdram controller in VHDL combinations.

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There is something wrong with quickswich devices. As I know MC68000 cant support 3.3V (some versions can but mine just cant). When i use quickswich any type i only get 5V to 3.3V translation and no vice versa. I need to use dual voltage level translator with auto sensing. Only parts that I can found with this is sn74lvc8t245 and new one like I write before txs0108e. For last two days I m reading about Pericom articles and those articles are just like IDT have for quickswich part. Devices are working from higher to lower and I m thinking that I just cant use those devices. For some devices who work with 5V can drive lower voltage levels that is ok but on my situation is not. For example PI5CX and PI3CX series are only related to 5V to 3.3V translation no bidirectional and then i need to use bus enable input like on most devices. From A to B bus or from B to A bus, that is not practical. Also some Pericom devices PI74LVC4245 who have two voltage on each bus side but no auto sensing again I need to set direction sides. I just dont know, as much i m reading only thing is txs0108e that I m using on design right now. Also using Pericom or IDT devices we can use pull up resistor connected to higher power source. I just dont know....

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