Max 232 and max 3232 communication

[raman00084]

i am communicating ds pic 5v (30f6010a) with rasberry pye in uart (rs232 communication). in ds pic i am using max232 ic that works on 5v power supply, in rasberry pye i am using max3232 ic that works on 3.3v level. it is possible to communicate both ics that is connecting tx of max 232 to rx of max3232 and rx of max 232 to tx of max 3232?

my doubt is one ic works on 5v and another on 3.3v but both outputs are rs232 level so communicating between 2 ic will not be a problem?

regards
kalyan

 

[paulfjujo]

hello,


Max3232 is requiered when using 3,3V to 5V power supply

confirmed in datasheet!

The MAX3222/MAX3232/MAX3237/MAX3241 transceivers
have a proprietary low-dropout transmitter output
stage enabling true RS-232 performance from a
3.0V to 5.5V supply with a dual charge pump. The
devices require only four small 0.1µF external chargepump
capacitors. The MAX3222, MAX3232, and
MAX3241 are guaranteed to run at data rates of
120kbps while maintaining RS-232 output levels.

 

[LoweReception]

Try taking a look at the datasheet/pinout of the Pi. I believe that the real problem here has to do with the external/internal voltage thresholds of the Pi.
Are the pins associated with UART Rx/Tx rated as 5V tolerant?
Does the Pi accept 5V as an acceptable logic 1?
If not, you could try bucking the voltage down through a regulator or a simple voltage divider.

 

[betwixt]

If I understand the first post, the question is "can the RS232 side of the two devices talk to each other". The answer is yes, that is exactly what they are intended to do.

The 'TTL' side of the MAX232 and MAX3232 must of course work at the supply voltages of their connected hosts.

Brian.

 

[D.A.(Tony)Stewart]

The RS-232 interface is inverted logic from the UART and is bipolar in signal level.

The good news is RS-232 uses the same threshold as TTL or 2 PN junction drops (1.3V) so +/-3.3 to +/- 15 ought to work, but of course noise immunity is compromised. So as long as your signal integrity is good, there should be no problems.

Twisted pair with common grounds and a balun for long lines ought to be enough. But watch out for SMPS chargers on mobile units (e.g. Pi & laptops) They can induce a CM noise interference when not earthed or connected to a large ground plane.