I use 74LVC245AN (a level shifter), suppose similar as 74LVC3245. However,
today I make all the connection between my 5V TTL sensor to 3.3V TTL TS7800
serial port using this level shifter, I got the same garbage data problem.
Seems strange that this problem doesn't go away...seem that I am trying to
solve multiple problems or one unknown problem.
Don't anyone has manage to get a 5V TTL sensor to work with 3.3V TTL serial
port on TS7800. I tested my 3.3V TTL GPS sensor working with the TS7800 5V TTL
serial port though with the same C code. So I rule out any software problem.
Anyone know if there is a need to place an inverter before the level shifter to
invert the signal between 3.3V TTL and 5V TTL, like the inversion done in RS232
standards from TTL?
?????
--- In "Ferenc Mikula" <> wrote:
>
>
> 74lvc3245 ??
>
>
> --- In "teohoeeng" <teohoeeng@> wrote:
> >
> > Thanks. I have looked at the MAXIM 300X datasheets you indicated. But I
> > think its Vih is too high for TTL level. The data sheets also seems to
> > suggest it is more for CMOS interface than TTL. I can't find any 3.3V TTL
> > to 5V TTL level shifter in maxim website...all those chips are meant for
> > CMOS which has a very high VIh compared to TTL.
> >
> > So difficult to find one suitable one....But I like the maxim 300X series
> > which allows bi-directional data transfer without needing direction bit,
> > and the interface is neat, requiring only power supply and data bit lines.
> > No need any cumbersome clk signal....
> >
> > One strange thing is that from tech support in TS, they said that the
> > serial port on TS7800 3.3V TTL is 5V tolerant upon OS bootup and I have
> > checked that those VIH, VOH, VIL and VOL for 3,3V and 5V TTL are the same.
> > If that's the case, it seems to suggest I shouldn't need any translator at
> > all...but I can TX to sensor but receive garbage from sensor....
> >
> > Still searching....Have anyone else tried any level shifter successfully
> > from TS7800 3.3V TTL to 5V TTL serially (bi-directional)
> >
> > --- In "Theodore A. Roth" <taroth@> wrote:
> > >
> > > On Sat, Mar 14, 2009 at 4:45 PM, teohoeeng <teohoeeng@> wrote:
> > > > Yes, I want to interface between 3.3V TTL UART and 5V TTL UART without
> > > > using any RS232 shifter to reduce hardware parts. I am only concern
> > > > with 3 lines, TX, RX and GND.
> > > >
> > > > In fact, my 5V TTL sensor can receive data possibly because the 3.3V
> > > > logic output still meet 5V TTL input requirements, but not the other
> > > > way round, that's why I cannot receive the data out from 5V sensor
> > > > output into the TS7800 3.3V TTL UART. I think I just need to meddle
> > > > with this RX line and leave the TX line untouched. I am reading my old
> > > > digital system notes now ot review those Voh, Vih, Ioh, Iih which I
> > > > have to use to size up the interface circuits or resistor....
> > > >
> > > > I also read in maxim website that simple resitor voltage divider with
> > > > diode can help to do that...but I just want to verify by calculting if
> > > > the resistors used will be compatible to my interface...
> > > >
> > > > I believ there are some standard resistance values to use for 3.3V TTL
> > > > to 5V TTL serial interface to use...I am checking and trying to
> > > > calculate now....
> > >
> > >
> > > I've used a MAX3100E (a bi-directional level shifter) to interface a
> > > 2.8V gsm modem uart to 3.3V lpc2378 uart. The gsm modem was not 3.3v
> > > tolerant. The MAX300X devices have a 1.2V - 5.5V range on VL and 1.65V
> > > - 5.5V VCC range. Should easily work for your application.
> > >
> > > http://www.maxim-ic.com/quick_view2.cfm/qv_pk/3672
> > >
> > > Ted Roth
> > >
> >
>
------------------------------------
Yahoo! Groups Links
<*> To visit your group on the web, go to:
http://groups.yahoo.com/group/ts-7000/
<*> Your email settings:
Individual Email | Traditional
<*> To change settings online go to:
http://groups.yahoo.com/group/ts-7000/join
(Yahoo! ID required)
<*> To change settings via email:
<*> To unsubscribe from this group, send an email to:
<*> Your use of Yahoo! Groups is subject to:
http://docs.yahoo.com/info/terms/
|