Battery ground, RS232

[Boki]

Hi All,

I use RS232 to connect PC and a embedded device.

Can I only connect TX and RX lines?

I am considering the GND maybe different, could you please advice?

Thank you very much!

Best regards,
Boki.

 

[Luhan]

Hi All,

I use RS232 to connect PC and a embedded device.

Can I only connect TX and RX lines?

I am considering the GND maybe different, could you please advice?

Thank you very much!

I am thinking the GND may be necessary.

Luhan

 

[Pooh Bear]

Hi All,

I use RS232 to connect PC and a embedded device.

Can I only connect TX and RX lines?

You *can* for sure.

Graham

 

[Pooh Bear]

I am considering the GND maybe different, could you please advice?

The PC and embedded device are at different potentials ? That might be a problem
! I'd fix that first.

Graham

 

[Boki]

Pooh Bear 寫�：

The PC and embedded device are at different potentials ? That might be a problem
! I'd fix that first.

Graham

Hi Graham,

I have connected GND, but still can't work.
Always got wrong data, does it possible PC's voltage level can't
sutable embedded device's ?

Best regards,
Boki.

 

[Pooh Bear]

Pooh Bear 寫�：


Hi Graham,

I have connected GND, but still can't work.
Always got wrong data, does it possible PC's voltage level can't
sutable embedded device's ?

RS232 supports a range of voltage levels. What's the RS232 interface chip in the
embedded device ?

Graham

 

[Boki]

Pooh Bear 寫�：

RS232 supports a range of voltage levels. What's the RS232 interface chipin the
embedded device ?

Graham

Hi,

Not sure, but my embedded device is 3.3V power supply.
Should I do anything to meet PC?

Thank you very much!

Best regards,
Boki.

 

[Clifford Heath]

Not sure, but my embedded device is 3.3V power supply.
Should I do anything to meet PC?

You almost certainly need an RS-232 level shifter, like one of
the MAX232 type ICs. RS232 signals coming out of most micros are
*positive* logic swinging between 0 and Vcc, whereas RS-232 requires
negative logic with negative swings - + and - 10V is common, but
a wide range is supported - +5 to -5 or even +5 to 0 are acceptable
to some equipment, though with lower noise and resistance to ground
imbalance problems. You can also roll your own level shifters,
including stealing the -ve rail from an incoming signal using a
diode and capacitor.

Please, no-one bitch about the exact definition of the RS-232
standards. I know there are standards, and that they're widely
flouted, and I don't care - I doubt Boki does either.

 

[Boki]

Clifford Heath 寫�：

You almost certainly need an RS-232 level shifter, like one of
the MAX232 type ICs. RS232 signals coming out of most micros are
*positive* logic swinging between 0 and Vcc, whereas RS-232 requires
negative logic with negative swings - + and - 10V is common, but
a wide range is supported - +5 to -5 or even +5 to 0 are acceptable
to some equipment, though with lower noise and resistance to ground
imbalance problems. You can also roll your own level shifters,
including stealing the -ve rail from an incoming signal using a
diode and capacitor.

Please, no-one bitch about the exact definition of the RS-232
standards. I know there are standards, and that they're widely
flouted, and I don't care - I doubt Boki does either.

Hi,

I just check the MAX232 data, the operation speed seems not high enough
for my app.

I am using 460.8Kbps ~ 921Kbps app, ( for this I have buy a PCI UART
card ...)

Any comment is appreciated!

Best regards,
Boki.

 

[Pooh Bear]

Pooh Bear 寫�：

Hi,

Not sure, but my embedded device is 3.3V power supply.
Should I do anything to meet PC?

If the embedded RS232 line driver can only output 3.3V it's no surprise that it doesn't
work. You really need to look at the interface chip. Are you using the RX and TX lines on
a processor directly by amny chance ?

Graham

 

[Boki]

Pooh Bear 寫�：

If the embedded RS232 line driver can only output 3.3V it's no surprise that it doesn't
work. You really need to look at the interface chip. Are you using the RXand TX lines on
a processor directly by amny chance ?

Graham

Yes... and now... I found the MAX232 is too slow for my this app..

<~~

Best regards,
Boki.

 

[Clifford Heath]

I just check the MAX232 data, the operation speed seems not high enough
for my app.

There are literally dozens of alternatives that all need different
sized (or no) external capacitors and have different maximum rates.
That's why I said "*like* one of the MAX232...". Almost every
manufacturer seems to make a variant now - I'm sure you can find one.

 

[Pooh Bear]

Hi,

I just check the MAX232 data, the operation speed seems not high enough
for my app.

I am using 460.8Kbps ~ 921Kbps app, ( for this I have buy a PCI UART
card ...)

Indeed a MAX232 isn't fast enough. Is this what you were using ?

Any comment is appreciated!

Do you actually need such a fast data rate ?

Graham

 

[Pooh Bear]

Pooh Bear 寫�：


Yes...

Naughty boy !

and now... I found the MAX232 is too slow for my this app..

Try looking at the PCI serial card you have to see what they use.

Graham

 

[Boki]

Pooh Bear 寫�：

Indeed a MAX232 isn't fast enough. Is this what you were using ?


Do you actually need such a fast data rate ?

Graham

I am sending jpg files. As faster as better.

I guess USB maybe better, but in order to meet Bluetooth SPP...

Best regards,
Boki.

 

[Rich Grise]

Pooh Bear

Hi Graham,

I have connected GND, but still can't work.
Always got wrong data, does it possible PC's voltage level can't
sutable embedded device's ?

"Getting Wrong Data" sounds like a baud rate mismatch.

Good Luck!
Rich

 

[Boki]

"Getting Wrong Data" sounds like a baud rate mismatch.

Good Luck!
Rich

Thanks, but that case...

Confusing, there is no ADM3202 near my place... any replacement?

Boki.

 

[Pooh Bear]

Confusing, there is no ADM3202 near my place... any replacement?

Plenty. Check that Google link I sent you. Intersil for example.

Graham

 

[tkirk]

Common problems connecting a PC to an embedded device:

1. Yes, you usually need the ground wire, unless you are running the PC
on the same power supply as the embedded device, in which case you
already have a ground wire coming in a different way.
2. If this is a laptop and you are out in the field, unplug the car
charger from the laptop. The inverters used can create nasty ground
loops that mess up communications and in rare occasions can blow up the
serial port on your embedded device.
3. Ensure you are running the correct software on your PC, that knows
the protocol to talk to the embedded device. Is your device talking
Modbus, AT modem commands, some proprietary protocol, etc?
4. Ensure no other software is running on the PC which might be using
the serial port. In general, only one program can use the serial port
at a time.
5. Ensure that the port settings match in the PC software and the
embedded device. Baud rate, parity, stop bits, etc. are important.
6. Some devices are expecting hardware handshaking on the serial port.
If this is the case, you either need to disable hardware handshaking,
or else hook up the extra pins needed on the serial port (RTS/CTS,
DTR/DSR, etc.) as well as just RX, TX, and GND.

Hope this helps!

Tim Kirk
[email protected]
Rogue Engineering Inc
http://www.rogue-engr.com