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Altera_Forum's avatar
Altera_Forum
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14 years ago

5V to 3.3V bus and vice versa

MC68000 to CycloneII

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 txs0108e even sn74lvc8t245 have direction control.

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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  • Altera_Forum's avatar
    Altera_Forum
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    14 years ago

    Yes but there are some old devices (hard to find now) who could capable of doing translations. This is all ok but i ll have also to try with PI5C34X245 from pericom also vith PI7C series and with QS32x245 from IDT. Also there is trusted QS3384. I ll get prototype PCB in 20 or so days and i ll report here my investigation. I think that this part of integration of old to new devices is not investigated, or we common people cant find informations. I was thinking that maybe this problem is simple one and noone take time to investigate it. Also production of devices goes up and they just dont want to interface new with old. Also voltages is going down, one day we might talk about interfacing 0.1V to 5V old system... As much I m reading about this for over past months I m thinking about that any bus translation device can work fine if you tune it in some other way, just we need to think about PCB space, and cost of production...

  • Altera_Forum's avatar
    Altera_Forum
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    14 years ago

    Unless you are trying to upgrade a legacy product, while trying to preserve a large software, or adapter board market, its unlikely that you would deliberately pair incompatible logic standards such as your MC68000 and a new generation FPGA.

    As you first pointed out, there are MC68000 devices with LVCMOS compatible logic interfaces, so I would expect most people to select that if they absolutely had to use an MC68000. Although, I would expect a new design to leverage ColdFire or something more closely compatible with the MC68000.

    In my designs, the FPGAs are used for signal processing. With a new generation FPGA, I can process significantly more data, and generally this means I have to transport more 'results' off the FPGAs. This in turn requires faster external buses, network interfaces, and hence a faster processor.

    Rather than reusing a specific processor, I try and update to the latest processor with a compatible instruction set, eg., in my case PowerPC processors from Freescale.

    Cheers,

    Dave
  • Altera_Forum's avatar
    Altera_Forum
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    14 years ago

    Yes that is what I was talking about. But for me problem is that I just cant replace MC68000 becouse they did not produced coldfire that can do that. It just cant emulate all the instructions and some are not the same. Maybe one day that I can manage to do some things about that.

  • Altera_Forum's avatar
    Altera_Forum
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    14 years ago

    --- Quote Start ---

    But for me problem is that I just cant replace MC68000 becouse they did not produced coldfire that can do that. It just cant emulate all the instructions and some are not the same. Maybe one day that I can manage to do some things about that.

    --- Quote End ---

    Yeah, I can understand. Good luck with your design.

    Cheers,

    Dave
  • Altera_Forum's avatar
    Altera_Forum
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    14 years ago

    These clamping devices need low ohmic pull-up to achieve sufficient speed at the high voltage side. This may be a problem with the drive strength of MC68000. But if the bus speed requirements aren't too high, it should work.

    In addition, I don't understand, why you can't generate a direction signal from the MC68000 bus control signals? Any kind of bus extenders does it.