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" <> wrote:
>
> On Sat, Mar 14, 2009 at 4:45 PM, 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
>
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