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....
--- In David Hawkins <> wrote:
>
> Hi,
>
> > Can anyone advise any good tutorial guide on using a level
> > shifter on how I can interface TS7800 3.3V TTL serial port
> > to a TTL 5V serial port of a sensor in bi-directional data
> > exchange? I can't find any comercial standalone product for
> > such converter, unlike the common one seen in RS232-TTL and vice-versa.
>
> Just to clarify your requirement, you want
> to directly connect a 3.3V UART to a 5V UART
> without using RS232 level shifters in between?
>
> ------ 3.3V ------------- 5V ------
> |UART#1|<---->|Level Shifter|<---->|UART#2|
> ------ ------------- ------
>
> The level shifter can be a 3.3V powered buffer that
> is 5V tolerant, or it can be a bus switch powered
> from 4.3V (a diode drop below 5V), and it'll clamp
> the 5V levels to around 3.3V.
>
> Fairchild TinyLogic parts are nice. Take a look at the
> NC7SZ125P5X buffer, or the NC7SZ384P5X bus switch.
>
> If you are interfacing a wider bus between 3.3V and 5V
> logic, there are many 3.3V buffers with 5V tolerant
> inputs.
>
> Cheers,
> Dave
>
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