hi
i have a device with RS232 communication port ,power supply is 9 volt in this device , but As you know Valid signals are either in the range of +3 to +15 volts or the range −3 to −15 volts with respect to the ground/common pin in RS232. do this power supply will not create any problem ?
when connect directly device to pc RS232 , Do not communicate with each other ! And sometimes drop power supply!
Do I must use the interface circuit ؟

 

If you use a MAX232 it has internal charge pump for the ±v .
Alternatively there are dedicated RS232 drivers & recievers that also require a separate ±v charge pump supply.
Max.

 

If you use a MAX232 it has internal charge pump for the ±v .

thanks MAX, in your opinion , i must use two MAX232?! (RS232 to ttl and ttl to RS232)
what is your order of internal charged pump in max232 ?

 

thanks MAX, in your opinion , i must use two MAX232?! (RS232 to ttl and ttl to RS232)
what is your order of internal charged pump in max232 ?

You would use one on the RX end and one on the TX end, what is meant by your order?
I have used them for some years now with excellent results.
Max.

 

Excuse me
I mean, why should I use MAX232? Why can not directly connect them to each other?(Both is RS232)
what is internal charged pump in max232 ? why must use separate ±v charge pump supply(Except max232)?

 

They can both be connected together TTL - RS232 then back RS232 - TTL on each end.
The older technology IC used a few decades ago required the separate charge pump.
Or do you mean keep at the TTL level?
Max.

 

I do not understand that why direct connection do not work!
why must first convert RS232 to ttl level and then ttl to RS232 level? why directly dont work?

 

I think you should provide some more infos and photos about your device to clarify what you described.

 

I think you should provide some more infos and photos about your device to clarify what you described.

 

Excuse me
I mean, why should I use MAX232? Why can not directly connect them to each other?(Both is RS232)
what is internal charged pump in max232 ? why must use separate ±v charge pump supply(Except max232)?

Buy some 2-terminal bi-colour LEDs and an equal number of 680R resistors - then you can wire up an RS232 connector as an indicator, then you can verify which line are inputs and which wires are outputs, that way you can make sure that you only connect outputs to inputs - then all you have to do is look up the right outputs to connect to which inputs.

Another possible source of confusion is the distinction between DCE and DTE, where DCE might be a modem and DTE might be the computer - the charts and tables weren't always consistent in how the pins were labled.

Search for "null-modem cable" you should find connection diagrams that with a bit of careful study, make the ins and outs fairly clear.

 

Buy some 2-terminal bi-colour LEDs and an equal number of 680R resistors - then you can wire up an RS232 connector as an indicator, then you can verify which line are inputs and which wires are outputs, that way you can make sure that you only connect outputs to inputs - then all you have to do is look up the right outputs to connect to which inputs.

if your mean is RX,TX and GND , Be sure to I've make the correct connections .

 

Too many reasons to caused them can't communicate each other, wrong baud rate, wrong port, wrong setting, etc...
What's your device?
I'm not sure why keeping it as secret, so we only can guessing the puzzle?

Too less infos ...

 

The program you are using in you PC may also be requesting hardware Handshake, if only using 3wire mode, you need to set XON/XOFF or no H.S., I usually jumper out the H.W. handshake on the P.C. side as a precaution.
This is 1-4-6 & 7-8 on a 9 pin D.
Max.

 

I'm not sure why keeping it as secret, so we only can guessing the puzzle?
Too less infos ...

my device is ABB aquamaster . Does not matter device name Because RS232 IS RS232
and I've done all the settings correct!

The program you are using in you PC may also be requesting hardware Handshake, if only using 3wire mode, you need to set XON/XOFF or no H.S.
Max.

i use hiper terminal with flow control set on NONE,
device side is 3 wire

This is 1-4-6 & 7-8 on a 5 pin D.
Max.

I did not test this.
I test a RS232 Isolator(Buy this) But It does not work !