Post by thread:[EE]: Interfacing to the ATA-interface

Hi. Does anyone in here know how to interface 3.3V logic to 5V logic? I have a PIC and some other stuff running at 3.3V , but need to interface with the ATA-interface from my PC, and a LCD-display, which both need 5V logic levels. Is there an easy way to do this? Or is it easier to run the PIC at 5V, and then convert the signals down to 3.3V? Or is it possible (yes, I say possible, not allowed) to just put it all together and operate the 5V logic devices at 3.3V ? Hans -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]: PIC only [EE]: engineering [OT]: off topic [AD]: advertisements

IMO, since your PIC is the main part here (comm with PC and LCD at 5V), I would say run it at 5V and convert down.The PIC will also still read a 3.3V input as Logic High. Quentin "H.P. de Vries" wrote: {Quote hidden}> > Hi. > > Does anyone in here know how to interface 3.3V logic to 5V logic? I have a > PIC and some other stuff running at 3.3V , but need to interface with the > ATA-interface from my PC, and a LCD-display, which both need 5V logic > levels. Is there an easy way to do this? Or is it easier to run the PIC at > 5V, and then convert the signals down to 3.3V? > Or is it possible (yes, I say possible, not allowed) to just put it all > together and operate the 5V logic devices at 3.3V ? > > Hans > > -- > http://www.piclist.com hint: PICList Posts must start with ONE topic: > [PIC]: PIC only [EE]: engineering [OT]: off topic [AD]: advertisements -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]: PIC only [EE]: engineering [OT]: off topic [AD]: advertisements

Ok, that would be my first thought also. This also seems like the least work, as I need to convert only about 5 lines, as opposed to the 24 5V signals I had otherwise to convert. But now, how do I convert the voltages down in an efficient way? I don't like the idea of putting zeners /w resistors on the outputs, since in that way I lose my low-impedance output of the pic. Did I mention I also have to drive an i2c-bus also at 3.3v? Now how do I go about that? I'm no i2c expert at all, so this is one part I for sure won't find an answer to myself easily. <sigh> Why don't all devices just run at 5V :-) Hans On Wed, Jul 05, 2000 at 11:26:48PM +0200, Quentin wrote: {Quote hidden}> IMO, since your PIC is the main part here (comm with PC and LCD at 5V), > I would say run it at 5V and convert down.The PIC will also still read a > 3.3V input as Logic High. > > Quentin > > "H.P. de Vries" wrote: > > > > Hi. > > > > Does anyone in here know how to interface 3.3V logic to 5V logic? I have a > > PIC and some other stuff running at 3.3V , but need to interface with the > > ATA-interface from my PC, and a LCD-display, which both need 5V logic > > levels. Is there an easy way to do this? Or is it easier to run the PIC at > > 5V, and then convert the signals down to 3.3V? > > Or is it possible (yes, I say possible, not allowed) to just put it all > > together and operate the 5V logic devices at 3.3V ? > > > > Hans > > > > -- > > http://www.piclist.com hint: PICList Posts must start with ONE topic: > > [PIC]: PIC only [EE]: engineering [OT]: off topic [AD]: advertisements > > -- > http://www.piclist.com hint: PICList Posts must start with ONE topic: > [PIC]: PIC only [EE]: engineering [OT]: off topic [AD]: advertisements > -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]: PIC only [EE]: engineering [OT]: off topic [AD]: advertisements

> -----Original Message----- > From: H.P. de Vries [SMTP:spam_OUTH.P.d.VriesTakeThisOuTSTUD.TUE.NL] > Sent: Wednesday, July 05, 2000 10:45 PM > To: .....PICLISTKILLspam@spam@MITVMA.MIT.EDU > Subject: Re: [EE]: Interfacing to the ATA-interface > > Ok, that would be my first thought also. This also seems like the least > work, as I need to convert only about 5 lines, as opposed to the 24 5V > signals I had otherwise to convert. > > But now, how do I convert the > voltages down in an efficient way? I don't like the idea of putting zeners > /w resistors on the outputs, since in that way I lose my low-impedance > output of the pic. > Did I mention I also have to drive an i2c-bus also at 3.3v? Now how do I > go > about that? I'm no i2c expert at all, so this is one part I for sure won't > find an answer to myself easily. > The Philips book "The I2C bus and how to use it" has a section on dealing with multi-voltage bus systems. The answer is amazingly simple and very elegant. A discreet mosfet is simply inserted in each line between the different voltage sections. The source connects to the three volt bus, drain to the 5 volt bus and gate to the 3.3v supply (Vdd). The operation isn't immediatley obvious (at least it wasn't to me) as part of the system relies on the internal diode accross a mosfet's drain/source, but I can report that it definately works. Cheers Mike {Quote hidden}> <sigh> > Why don't all devices just run at 5V :-) > > Hans > On Wed, Jul 05, 2000 at 11:26:48PM +0200, Quentin wrote: > > IMO, since your PIC is the main part here (comm with PC and LCD at 5V), > > I would say run it at 5V and convert down.The PIC will also still read a > > 3.3V input as Logic High. > > > > Quentin > > > > "H.P. de Vries" wrote: > > > > > > Hi. > > > > > > Does anyone in here know how to interface 3.3V logic to 5V logic? I > have a > > > PIC and some other stuff running at 3.3V , but need to interface with > the > > > ATA-interface from my PC, and a LCD-display, which both need 5V logic > > > levels. Is there an easy way to do this? Or is it easier to run the > PIC at > > > 5V, and then convert the signals down to 3.3V? > > > Or is it possible (yes, I say possible, not allowed) to just put it > all > > > together and operate the 5V logic devices at 3.3V ? > > > > > > Hans > > > > > > -- > > > http://www.piclist.com hint: PICList Posts must start with ONE topic: > > > [PIC]: PIC only [EE]: engineering [OT]: off topic [AD]: advertisements > > > > -- > > http://www.piclist.com hint: PICList Posts must start with ONE topic: > > [PIC]: PIC only [EE]: engineering [OT]: off topic [AD]: advertisements > > > > -- > http://www.piclist.com hint: PICList Posts must start with ONE topic: > [PIC]: PIC only [EE]: engineering [OT]: off topic [AD]: advertisements -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

imho, cut your design into 3.3 and 5 V parts such that: - you have no bidirectional lines crossing - you have the fewest possible lines crossing - you do not have fast data/clock lines crossing then look for an interface chip that will solve your problem, or use discretes. A 4 part/chip ancient CMOS chip exists that will do this, and there are many modern variants with up to 32 x per package, but they all require lots of power (even if only for switching). Among discretes, open collector digital transistor arrays are popular with me. One of those and a SIPP resistor array and you have 8 or 9 wires converted. Only works with slow signals, but phantom power is not a concern. Most other drivers have a problem with phantom power (i.e. what happens if one of the supplies is missing or if you power up or down in the wrong sequence). Peter -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

On Thu, Jul 06, 2000 at 08:59:10PM +0300, Peter L. Peres wrote: > >i2c bus at 3.3V > > If you use bit banged I2C then use a separate data in and out pin and you > are set. The data out only needs a shottky diode, the input a > (relatively large) resistor. The clock driver can have just a series > resistor. Most I2C components clamp the I2C pins efficiently to Vcc and > GND and are not bothered by this mode of operation. However, check ;-) > I saw another design which also uses just a resistor in series of the I2C data-line. I plan on using the I2C feature of the 16c87x -series. Is this also possible with just a series-resistor? The design I saw had a 100-ohms resistor in series. About the open-collector transistor solution : It should be something like : |Vdd (3.3v) [R] |_________ out signal (5V) |/c --[R]----| b |\e | |------- gnd (Great ASCII , isn't it?) Can I use this up to speeds of 1MHz, or do I need to search for special transitors then? Anyway, I don't think 3.3V inputs to the pic would really need converting. Doesn't it recognise 3.3v as high anyway? The only thing I then needed to convert was the input to the pic, as it probably won't really like the over-voltage on its inputs. Any suggestions? Hans -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

>> Does anyone in here know how to interface 3.3V logic to 5V logic? I >> have a PIC and some other stuff running at 3.3V , but need to interface >> with the ATA-interface from my PC, and a LCD-display, which both need >> 5V logic The simplest level translator I've seen (other than a resistor) is to use a bus switch device. The first one I located in Farnell was the Fairchild FST3244WM, though there are probably others. The devices consist of banks of N type FETS as pass gates. The usefull part is that the on resistance rises rapidly when a certain voltage is reached, and by running the device off slightly less than 5v (1 diode drop I believe but I've lost the circuit I saw) any signal will be clamped at around 3V. Below this the device has low on resistance and therefore will pass fast signals. Because the device is purely a switch it is fully bidirectional and should not be affected by floating signals. I haven't tried this, it came from a circuit ideas booklet I got a couple of years ago. RE LCDs. My experience has been that the HD44780 LCD driver will run from 3.2v, although such use appears undocumented. The snag is the display will be barely visible. There is a TRICK to get round this. Vo (contrast) CAN BE TAKEN BELOW GROUND! VCC-Vo determines contrast, so a weak negative supply restores contrast. Below 3V a test circuit still appeared to work (an old 16c84 seems nearly unstoppable) but the display faded anyway, so the logic is probably giving up. Oliver. -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.