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2005-05-06 by javida13
I have a 5 volt logical display that I'm driving. The Vol for this part is 3.5 volts (.7*Vcc). I have 3-signals that must be driven to this logic level. Is there a LS type of device that can be used as the level translator, where is can be powered by 5 volts and its input level can be driven by 3.3 volt logic? Barry
2005-05-06 by Robert Adsett
At 02:54 PM 5/6/05 +0000, javida13 wrote: >I have a 5 volt logical display that I'm driving. The Vol for this >part is 3.5 volts (.7*Vcc). I have 3-signals that must be driven to >this logic level. Is there a LS type of device that can be used as the >level translator, where is can be powered by 5 volts and its input >level can be driven by 3.3 volt logic? Standard HCT logic. TI has a good selection. I still remember fondly the yellow TI logic bible http://focus.ti.com/logic/docs/bytechnologyfamily.tsp?templateId=5985&navigationId=11386&path=templatedata/cm/ovw/data/hct_overview&technologyFamilyId=16 Other manufacturers, including Philips, should also have a good selection. Robert " 'Freedom' has no meaning of itself. There are always restrictions, be they legal, genetic, or physical. If you don't believe me, try to chew a radio signal. " -- Kelvin Throop, III http://www.aeolusdevelopment.com/
2005-05-06 by lpc2100_fan
Philips has a good selection too ;-) http://www.standardics.philips.com/products/hc/all/ Cheers, Bob --- In lpc2000@yahoogroups.com, Robert Adsett <subscriptions@a...> wrote: > At 02:54 PM 5/6/05 +0000, javida13 wrote: > >I have a 5 volt logical display that I'm driving. The Vol for this > >part is 3.5 volts (.7*Vcc). I have 3-signals that must be driven to > >this logic level. Is there a LS type of device that can be used as the > >level translator, where is can be powered by 5 volts and its input > >level can be driven by 3.3 volt logic? > > Standard HCT logic. > > TI has a good selection. I still remember fondly the yellow TI logic bible > > http://focus.ti.com/logic/docs/bytechnologyfamily.tsp?templateId=5985&navigationId=11386&path=templatedata/cm/ovw/data/hct_overview&technologyFamilyId=16 > > Other manufacturers, including Philips, should also have a good selection. > > Robert > > " 'Freedom' has no meaning of itself. There are always restrictions, be > they legal, genetic, or physical. If you don't believe me, try to chew a > radio signal. " -- Kelvin Throop, III > http://www.aeolusdevelopment.com/
2005-05-06 by Peter Jakacki
Vol ??? You do mean Vih, don't you? In my experience I've never had a problem with driving 5V logic from 3.3V as the minimum Vih in is specified for full-speed digital switching. The 3.3V definitely drives the 5V logic as a logic high but it may not work to "parametric" specification at 100Mhz etc. For all your normal I/O work it is never a problem and I don't let myself lose sleep over it. You can though for peace of mind and sleep use pull-up resistors to +5V on the output lines and simply simulate open-drain drivers by writing the IODIR. It doesn't matter if you initially drive them to 3.3V and then float by switching to inputs with the pull-up. IMO, skip the buffers, they are always overkill. my2cents *Peter* p.s. Hey Rob! I dug out the TI yellow bible and mine is dated 1988. I also remember my first logic data book, it was a big red Fairchild Semiconductor TTL data book from the early '70s. Back then you needed PSUs that could supply amps, none of this itsy-bitsy pencell battery stuff! Plus you had to worry about fanout (both the blower type and driving type). javida13 wrote:
>I have a 5 volt logical display that I'm driving. The Vol for this >part is 3.5 volts (.7*Vcc). I have 3-signals that must be driven to >this logic level. Is there a LS type of device that can be used as the >level translator, where is can be powered by 5 volts and its input >level can be driven by 3.3 volt logic? >
2005-05-07 by javida13
Yes, I did mean VIH. I forgot to preview before I posted. I'm interfacing to a Futaba LCD Emulator. Some of the inputs are spec'ed at 0.8*Vcc and others are at 0.7*Vcc Min. I checked with an App Eng at Futaba USA and he indicated that 3.3 volt logic will not drive the device. Since I only have 3-signals to this device (serial interface), its probably safe to use a AHCT125 device. The only problem is that the data I/O line is bi-directional therefore an additional GPIO is required for this input. Barry Peter Jakacki <peterjak@t...> wrote: > Vol ??? You do mean Vih, don't you? In my experience I've never had a > problem with driving 5V logic from 3.3V as the minimum Vih in is > specified for full-speed digital switching. The 3.3V definitely drives > the 5V logic as a logic high but it may not work to "parametric" > specification at 100Mhz etc. For all your normal I/O work it is never a > problem and I don't let myself lose sleep over it. > > You can though for peace of mind and sleep use pull-up resistors to +5V > on the output lines and simply simulate open-drain drivers by writing > the IODIR. It doesn't matter if you initially drive them to 3.3V and > then float by switching to inputs with the pull-up. IMO, skip the > buffers, they are always overkill. > > my2cents > *Peter* > > p.s. Hey Rob! I dug out the TI yellow bible and mine is dated 1988. I > also remember my first logic data book, it was a big red Fairchild > Semiconductor TTL data book from the early '70s. Back then you needed > PSUs that could supply amps, none of this itsy-bitsy pencell battery > stuff! Plus you had to worry about fanout (both the blower type and > driving type). > > > javida13 wrote: > > >I have a 5 volt logical display that I'm driving. The Vol for this > >part is 3.5 volts (.7*Vcc). I have 3-signals that must be driven to > >this logic level. Is there a LS type of device that can be used as the
> >level translator, where is can be powered by 5 volts and its input > >level can be driven by 3.3 volt logic? > >
2005-05-07 by Richard Duits
You can also use a pull up resistor to 5 volt, and switch the gpio between low output and input. This works because the GPIOs are 5 volt tolerant (don't do this with an adc capable pin, see the errata for explanation). Richard Duits. javida13 wrote:
> Yes, I did mean VIH. I forgot to preview before I posted. I'm > interfacing to a Futaba LCD Emulator. Some of the inputs are spec'ed > at 0.8*Vcc and others are at 0.7*Vcc Min. I checked with an App > Eng at Futaba USA and he indicated that 3.3 volt logic will not drive > the device. Since I only have 3-signals to this device (serial > interface), its probably safe to use a AHCT125 device. The only > problem is that the data I/O line is bi-directional therefore an > additional GPIO is required for this input. > > Barry > > Peter Jakacki <peterjak@t...> wrote: > > Vol ??? You do mean Vih, don't you? In my experience I've never had > a > > problem with driving 5V logic from 3.3V as the minimum Vih in is > > specified for full-speed digital switching. The 3.3V definitely > drives > > the 5V logic as a logic high but it may not work to "parametric" > > specification at 100Mhz etc. For all your normal I/O work it is > never a > > problem and I don't let myself lose sleep over it. > > > > You can though for peace of mind and sleep use pull-up resistors to > +5V > > on the output lines and simply simulate open-drain drivers by > writing > > the IODIR. It doesn't matter if you initially drive them to 3.3V > and > > then float by switching to inputs with the pull-up. IMO, skip the > > buffers, they are always overkill. > > > > my2cents > > *Peter* > > > > p.s. Hey Rob! I dug out the TI yellow bible and mine is dated 1988. > I > > also remember my first logic data book, it was a big red Fairchild > > Semiconductor TTL data book from the early '70s. Back then you > needed > > PSUs that could supply amps, none of this itsy-bitsy pencell > battery > > stuff! Plus you had to worry about fanout (both the blower type and > > driving type). > > > > > > javida13 wrote: > > > > >I have a 5 volt logical display that I'm driving. The Vol for > this > > >part is 3.5 volts (.7*Vcc). I have 3-signals that must be driven > to > > >this logic level. Is there a LS type of device that can be used as > the > > >level translator, where is can be powered by 5 volts and its input > > >level can be driven by 3.3 volt logic? > > > > > > > ------------------------------------------------------------------------ > *Yahoo! Groups Links* > > * To visit your group on the web, go to: > http://groups.yahoo.com/group/lpc2000/ > > * To unsubscribe from this group, send an email to: > lpc2000-unsubscribe@yahoogroups.com > <mailto:lpc2000-unsubscribe@yahoogroups.com?subject=Unsubscribe> > > * Your use of Yahoo! Groups is subject to the Yahoo! Terms of > Service <http://docs.yahoo.com/info/terms/>. > >
2005-05-07 by Marko Pavlin (home)
I designed one automatic-test circuit with 3-5V preipheral (device tested). The MCU was LPC932. I used GTL2000 for level shifting. It worked fine, even for higher speed signals (SPI). http://www.semiconductors.philips.com/pip/GTL2000DGG.html GTL2000 is 22 bit, there are versions with less lines/smaller package. Mare Richard Duits wrote:
> You can also use a pull up resistor to 5 volt, and switch the gpio > between low output and input. This works because the GPIOs are 5 volt > tolerant (don't do this with an adc capable pin, see the errata for > explanation). > > Richard Duits. > > > javida13 wrote: > > > Yes, I did mean VIH. I forgot to preview before I posted. I'm > > interfacing to a Futaba LCD Emulator. Some of the inputs are spec'ed > > at 0.8*Vcc and others are at 0.7*Vcc Min. I checked with an App > > Eng at Futaba USA and he indicated that 3.3 volt logic will not drive > > the device. Since I only have 3-signals to this device (serial > > interface), its probably safe to use a AHCT125 device. The only > > problem is that the data I/O line is bi-directional therefore an > > additional GPIO is required for this input. > > > > Barry > > > > Peter Jakacki <peterjak@t...> wrote: > > > Vol ??? You do mean Vih, don't you? In my experience I've never had > > a > > > problem with driving 5V logic from 3.3V as the minimum Vih in is > > > specified for full-speed digital switching. The 3.3V definitely > > drives > > > the 5V logic as a logic high but it may not work to "parametric" > > > specification at 100Mhz etc. For all your normal I/O work it is > > never a > > > problem and I don't let myself lose sleep over it. > > > > > > You can though for peace of mind and sleep use pull-up resistors to > > +5V > > > on the output lines and simply simulate open-drain drivers by > > writing > > > the IODIR. It doesn't matter if you initially drive them to 3.3V > > and > > > then float by switching to inputs with the pull-up. IMO, skip the > > > buffers, they are always overkill. > > > > > > my2cents > > > *Peter* > > > > > > p.s. Hey Rob! I dug out the TI yellow bible and mine is dated 1988. > > I > > > also remember my first logic data book, it was a big red Fairchild > > > Semiconductor TTL data book from the early '70s. Back then you > > needed > > > PSUs that could supply amps, none of this itsy-bitsy pencell > > battery > > > stuff! Plus you had to worry about fanout (both the blower type and > > > driving type). > > > > > > > > > javida13 wrote: > > > > > > >I have a 5 volt logical display that I'm driving. The Vol for > > this > > > >part is 3.5 volts (.7*Vcc). I have 3-signals that must be driven > > to > > > >this logic level. Is there a LS type of device that can be used as > > the > > > >level translator, where is can be powered by 5 volts and its input > > > >level can be driven by 3.3 volt logic? > > > > > > > > > > > > ------------------------------------------------------------------------ > > *Yahoo! Groups Links* > > > > * To visit your group on the web, go to: > > http://groups.yahoo.com/group/lpc2000/ > > > > * To unsubscribe from this group, send an email to: > > lpc2000-unsubscribe@yahoogroups.com > > <mailto:lpc2000-unsubscribe@yahoogroups.com?subject=Unsubscribe> > > > > * Your use of Yahoo! Groups is subject to the Yahoo! Terms of > > Service <http://docs.yahoo.com/info/terms/>. > > > > > > > > *Yahoo! Groups Links* > > * To visit your group on the web, go to: > http://groups.yahoo.com/group/lpc2000/ > > * To unsubscribe from this group, send an email to: > lpc2000-unsubscribe@yahoogroups.com > <mailto:lpc2000-unsubscribe@yahoogroups.com?subject=Unsubscribe> > > * Your use of Yahoo! Groups is subject to the Yahoo! Terms of > Service <http://docs.yahoo.com/info/terms/>. > >