Interfacing 5v to 3.3V UART

[GNU]

Hello,
I want to comminicate two UARTs : 3.3V (UART1 Vinmax = 3.7V) with a TTL
one (UART2 5V) from 9600Baud to 250Kb/s like this :

UART1 (TTL 5V) UART2 (3.3V)
TX1 ------------> RX2
RX1 <----------- TX2

From TX2->RX1, i think there's no problčme. My question is how to
interface Tx1&RX2, The first sends 5v to Rx2 wich accepts only 3.3
signals. Need your help please.
Thanks.
Tarek

 

[Soeren]

Hi Tarek,

GNU <Reply_In_NG_Please> wrote in newspr82gipcd0l9kb4@alata:

Hello,
I want to comminicate two UARTs : 3.3V (UART1 Vinmax = 3.7V) with a
TTL one (UART2 5V) from 9600Baud to 250Kb/s like this :

UART1 (TTL 5V) UART2 (3.3V)
TX1 ------------> RX2
RX1 <----------- TX2

From TX2->RX1, i think there's no problčme.

That depends on the hi/lo-levels, but you might get away with a direct
coupling (if not, add 2 transistors to convert the voltages).

My question is how to
interface Tx1&RX2, The first sends 5v to Rx2 wich accepts only 3.3
signals. Need your help please.

Use a resistor and a zener diode like this:

TX1 ---[1k5]---+----- RX2
__|__/
/ /_\ Z3V3
|
Gnd -----------+----- Gnd


--
Regards,
Soeren

* If it puzzles you dear... Reverse engineer *
New forum: <URL:http://www.ElektronikTeknolog.dk/cgi-bin/SPEED/>