interfacing to "another" system

[Antonis Konstantinos]

Hi All,

I am now building a system which will be communicating to another
system via UART at low rates (4800 bps)

The board that I am building will be powered up from an SMPS and the
other system has its own power supply. I plan to connect the uart
lines directly (without any buffer, optocoupler etc.) to my micro and
connect the ground of each system together.

Both systems uses 5V logic.

I have already built the system and it works fine *for now*.

Do you think that there is a more appropriate way of doing this? If so
what would you recommend ?

Thanks in advance,

Regards

 

[Leon Heller]

Hi All,

I am now building a system which will be communicating to another
system via UART at low rates (4800 bps)

The board that I am building will be powered up from an SMPS and the
other system has its own power supply. I plan to connect the uart
lines directly (without any buffer, optocoupler etc.) to my micro and
connect the ground of each system together.

Both systems uses 5V logic.

I have already built the system and it works fine *for now*.

Do you think that there is a more appropriate way of doing this? If so
what would you recommend ?

It depends on how far apart they are.

Leon

 

[scada]

Hi All,

I am now building a system which will be communicating to another
system via UART at low rates (4800 bps)

The board that I am building will be powered up from an SMPS and the
other system has its own power supply. I plan to connect the uart
lines directly (without any buffer, optocoupler etc.) to my micro and
connect the ground of each system together.

Both systems uses 5V logic.

I have already built the system and it works fine *for now*.

Do you think that there is a more appropriate way of doing this? If so
what would you recommend ?

Thanks in advance,

Regards

A fiber optic link would allow you the best communication speeds, and afford
total electrical isolation between the two systems. You can get copper to
fiber converters, or make your own. Check with LComm, Black Box, etc.. (both
are .com's)

 

[Frank Bemelman]

Hi All,

I am now building a system which will be communicating to another
system via UART at low rates (4800 bps)

The board that I am building will be powered up from an SMPS and the
other system has its own power supply. I plan to connect the uart
lines directly (without any buffer, optocoupler etc.) to my micro and
connect the ground of each system together.

Both systems uses 5V logic.

I have already built the system and it works fine *for now*.

Do you think that there is a more appropriate way of doing this? If so
what would you recommend ?

If it is a fixed setup, and never gets unplugged, such as inside
a machine, it's okay.

 

[Jan Panteltje]

Hi All,

I am now building a system which will be communicating to another
system via UART at low rates (4800 bps)

The board that I am building will be powered up from an SMPS and the
other system has its own power supply. I plan to connect the uart
lines directly (without any buffer, optocoupler etc.) to my micro and
connect the ground of each system together.

Both systems uses 5V logic.

I have already built the system and it works fine *for now*.

Do you think that there is a more appropriate way of doing this? If so
what would you recommend ?

Thanks in advance,

Regards

You could use MAX232 ICs to make the level rs232 compatible.
So then you can use the PC serial port to test...
The signal to noise would improve from it too.
JP

 

[Rich Grise]

[email protected] (Antonis Konstantinos) wrote in
You could use MAX232 ICs to make the level rs232 compatible.
So then you can use the PC serial port to test...
The signal to noise would improve from it too.

I've seen discrete transistors used as line drivers for "RS232" lines,
like complementary emitter-followers with enough series resistance
to make them short-immune, and it may have even acted like sort of a
terminator - and series resistors and protection diodes to the xsitor
bases on the receiving end.

This may be overkill, depending on the app.

Good Luck!
Rich

 

[Tim Hubberstey]

Hi All,

I am now building a system which will be communicating to another
system via UART at low rates (4800 bps)

The board that I am building will be powered up from an SMPS and the
other system has its own power supply. I plan to connect the uart
lines directly (without any buffer, optocoupler etc.) to my micro and
connect the ground of each system together.

This is where your potential problem lies. A direct logic-level
connection between 2 systems with independent power supplies will be
subject to power sequencing problems. Since both devices are most likely
CMOS, there is a very real risk of causing destructive latchup of one of
the inputs.

Some sort of buffering to ensure safe levels while either system is
powered off is required. For the data rate you're using, an open
collector driver with a pull-up to the receiving side's power supply
should be adequate.

 

[Antonis Konstantinos]

It depends on how far apart they are.

at most 20cm apart. connected with a flat cable. (like the ones used
to connect Hard Drives in the PC)

 

[Antonis Konstantinos]

If it is a fixed setup, and never gets unplugged, such as inside

a machine, it's okay.

Well I can say it will not be unplugged as long as it works. But what
is the idea behind that? Can you explain a bit further ?

Thanks

 

[Frank Bemelman]

Well I can say it will not be unplugged as long as it works. But what
is the idea behind that? Can you explain a bit further ?

Floating stuff, static charged users, etc. Similar to parallel
printerports on PC's that sometimes get fried. Never happens
when trying to demonstrate it, but it does happen when you
don't expect it

But as another poster pointed out, you also have the issue of
powerup sequence, so it is not such a good idea to connect it
directly.

 

[Jan Panteltje]

I've seen discrete transistors used as line drivers for "RS232" lines,
like complementary emitter-followers with enough series resistance
to make them short-immune, and it may have even acted like sort of a
terminator - and series resistors and protection diodes to the xsitor
bases on the receiving end.

This may be overkill, depending on the app.

Good Luck!
Rich

Yes this is possible, the MAX232 makes nice plus and minus voltages for
you from +5V however.
Only needs a couple of electrolytics.
JP

 

[Ken Smith]

Yes this is possible, the MAX232 makes nice plus and minus voltages for
you from +5V however.
Only needs a couple of electrolytics.

LT1181 uses ceramics.

 

[Jan Panteltje]

On a sunny day (Fri, 21 May 2004 18:22:23 +0000 (UTC)) it happened

LT1181 uses ceramics.

Those are cheaper?