[PIC] Distance between UART

[erpgc82]

Hello friends, can someone with experience tell me what is the maximum distance that I can use 2 PIC communicating, without using the MAX232 chip?

Connect the PIC18F46K22 to the PIC16F628.
TX ------------------------------------ RX
RX ------------------------------------ TX
Without using MAX232, directly with an 80cm cable. Will I have problems?

Thanks!

 

[KlausST]

Hi,

It depends on
* baud rate
* wiring
* cable type
* possible termination
* filters
* introduced noise
* threshold levels
* ...
We can not know all this, unless you tell us.
This makes helping difficult.

Some UART communication have problems with 20cm, others work well with 20m.

Additionally it depends on safety issues of your application and on error tolerant protocol.

Klaus

Added:
Besides the data lines you need to connect GND. Both for TTL levels and RS232 levels.

 

[erpgc82]

Hello friend Mrs. Kaus, answering:

My transmission/reception rate will be 9.6Kbps

The wire used will be those colored flat cables, with 4 ways, known as "DUPONTO" or for connection in "PIN HEADER"

It will not be the cable with mesh, or aluminum cap.

the size will be 800mm maximum size (80cm)

I have no knowledge about noises!
I'm a beginner in firmware programming, but I've been making PCBs since the time of TANGO, 90's!
I had never before created something like this without the MAX232.

In tests here, it's working normally, my question is about the future, will I have problems!

 

[danadakk]

Build a prototype with actual cable and loads, and examine timing to see if
logic noise margins and timing are met with plenty, say 100%, tolerance. In-
troduce noise into system, to see how robust protocol and HW is.

And consider fault conditions, if this is life support or potential to harm
people then protocol and HW must meet safety concerns.

Regards, Dana.

 

[erpgc82]

Build a prototype with actual cable and loads, and examine timing to see if
logic noise margins and timing are met with plenty, say 100%, tolerance. In-
troduce noise into system, to see how robust protocol and HW is.

And consider fault conditions, if this is life support or potential to harm
people then protocol and HW must meet safety concerns.

Regards, Dana.

Hi Dana, it's not equipment related to health or life...

Thank you for the tips!

I will test deeply, thanks!!!!!

 

[Aussie Susan]

Also see https://www.microchip.com/forums/m1178079.aspx where the question is marked as 'answered'
Susan

 

[KlausST]

Hi,

Why don't you use RS232, or RS485?

A simple logic gate is not designed to drive 80cm cable.
But indeed I see no problem to make it work.

A 100 Ohms series resistor and ESD protection diodes on the transmitter side (maybe a capacitor to limit rise/fall rate)
A ESD protection, low pass filter and a schmitt trigger on the receiver side.
..
And I see no problem for 80cm, not for usual noise levels.. and not for the future.
Future: what can we expect? Increasing frequencies, but not higher noise levels.
And the low pass filter should be able to attenuate high frequencies.

But what do you gain?
With the additional parts you don't save much space and cost.
The additional parts usually are already inside true "interface driver ICs".

RS232 isn't the most modern interface, but for your application it should work without problems.

Klaus