Serial comunication

[Zener_Diode]

Hey.
I have a device that conneted to serial port. I need to know its RX and TX data.
I wanna rewrite its program to work under windows.
when I connected scope to RX and TX pins I saw strange thing. I have Tx and RX at the same time and the same logic levels! Tx have amplitude +12Vto -12V and RX have ampitude 0 to +5V.

Why I see Tx and Rx and the same time?
how can I know what is tx and what is rx?


thanks ahead.

 

[lord loh.]

I am not an expert.

What device is this ?
Was it behaving so under the control of your programme ?

Are you absolutely sure that there was no error in measurement with the oscilloscope ?
Could it be a ground / loop problem ?

 

[Zener_Diode]

It is a motorola (HT1000) programmer. I mesure tx and rx when i try to read\send\test setup from its dos program.

I don't think that any error exist, because when I touch a probe I see the signal at one channel.

 

[tansis]

I've got a very old copy of "quick basic 3" if you need it, designed for DOS it will run under windows , but not fully tested under XP and its dammed firewall settings.

(downside is low res graphics and no mouse support)

 

[elec_lover]

The standard is -12 - +12 volt. but to save battery power some portable pc's are driving -3 to +3 volt. If you see 0 to +5 Volt the the (hardware)driver of the -5 Volt might be broken.
How to find tx signal ? When you disconnect the cable ande there is no data transfer, the signal is negative if pulled up by a resistor of 10K to ground.

 

[Zener_Diode]

everything is work, so nothing is broken!!!!!!!
I use the original program.

when I disconnect the the device I can see only the Tx data. but when device is connected I see the same data at both channels.

why I see the same data????
How can I what is TX data and what is rx data????

 

[elec_lover]

A lot of communication equipment are using "echo", all receive bytes are send back.

 

[lord loh.]

It is a motorola (HT1000) programmer. I mesure tx and rx when i try to read\send\test setup from its dos program.

I don't think that any error exist, because when I touch a probe I see the signal at one channel.

Looks like Zener_diode doesn't want it... But if any one is intrested, I have got QBasic 7. It can compile to a .exe

Echo all recieved bytes ? But you ought to first receive them isn't it ? But Zener_diode says that he sees tham at the same time on the osiclloscope.

Could checking out the RFC of the protocol be worth the time ?

 

[Zener_Diode]

what is RFC protocol????

 

[lord loh.]

what is RFC protocol????

RFC of the protocol.

RFC- Requent for comments. Whenever someone wants to develop a protocol or standard specification they post a draft and ask for comments. Make a google search for RFC (**broken link removed** doesnt seem to be opening.)

If the protocol your device is using is listed there it shall have 100% explainations of all the things that are happening.

 

[free1]

Hey.
I have a device that conneted to serial port. I need to know its RX and TX data.
I wanna rewrite its program to work under windows.
when I connected scope to RX and TX pins I saw strange thing. I have Tx and RX at the same time and the same logic levels! Tx have amplitude +12Vto -12V and RX have ampitude 0 to +5V.

Why I see Tx and Rx and the same time?
how can I know what is tx and what is rx?


thanks ahead.

Hi there,

When RS232 transmit signals TX will at level -12 to +12, but when it receives any signals RX, it will convert it to TTL level 0V or 5V with voltage level converter. Because most of IC only operate on TTL level.

free 8)

free

 

[Zener_Diode]

And why I see Tx and Rx at the same time from the first bit????
how can I know what is Tx data and what is Rx one???

 

[Nigel Goodwin]

And why I see Tx and Rx at the same time from the first bit????

As already mentioned, it's simply echoed back - if they are at EXACTLY the same time, it's obviously a hardware echo - with the TX and RX simply connected together.

how can I know what is Tx data and what is Rx one???

By the pins they use!.

 

[Zener_Diode]

The dont connected together because the volt lavels are different.
I see on both cannels the same data, how should I know what is send data ans what is received data?

 

[mstechca]

Assuming the device is digital, take two LED's, any two colours. Hook one up to TX and ground and hook the other one to RX and ground. Start your device and make it send data to the port. If one light isn't flashing on and off randomly, then try switching GND with +ve (in other words, connect the LED's to +ve) and try again. Either way, when you make your device send data to the port, one led should blink. If it doesn't, your LED is dead and u must use another LED.

The LED that goes on and off randomly is the result of the TX line.

 

[Nigel Goodwin]

The dont connected together because the volt lavels are different.

It depends where they connect - if I was doing it with a MAX232 I'd connect the 5V side, NOT the +/-12V side.

How accurately are you measuring the data?, if it's absolutely simultaneous it's got to be hardware echo - if it's a few uS apart it could be software echo (echoing each individual bit, rather than each byte).

I see on both cannels the same data, how should I know what is send data ans what is received data?

If it's the same data it's most probably data sent from the PC, it's not so common to have the PC echo back data that the programmer sends it.

 

[Zener_Diode]

I know what is tx and what is rx!!!!!!!
when I wanna see(ON SCOPE) the data that TX send and the data that RX receive, I see the same data on Tx and Rx (the same logic levels!!!).

 

[Nigel Goodwin]

I know what is tx and what is rx!!!!!!!
when I wanna see(ON SCOPE) the data that TX send and the data that RX receive, I see the same data on Tx and Rx (the same logic levels!!!).

I'm still rather vague what you're trying to do?.

You've scoped the data on TX and RX, and you say they are the same (in which case, as you've been repeatedly told, the data is being echoed - a common occurance in RS232). So you already know what ALL the data is (at least as far as you can see it on a scope!) - if you want to know ONLY the received data (that sent back from the programmer) you will need to filter out the echoed data.

But in any case, none of this can really be done with a scope, you need another PC connected monitoring the data line back from the programmer. Monitor the data back from the programmer and save it to a file, then do the same (with the identical program data) on the transmit line, again save it to a file. Then compare the two files!.

What are you trying to do anyway?.

 

[Zener_Diode]

I have a burning motorola program. The program run under dos. I want to rewrite in under windows.

Q: Why I wanna do it???
A: when I burn motorola HT1000 I need to read it, change the freq I want and then write it back. When I need to burn 50 motorols it takes a lot of time.
My program won't ask to read each motorola before I burn it. thats mean that I can give the freq I wanna burn, and I will burn it to 50 devices without read every one and change its freq and burn it again.

Now, do you understand me????


Some told me that I can write (or download a TSR program). That program "steals" serial comunication port inetupt, and give me an option to read the send\receive data before the interupt occure.
But I don't know where can I get this TSR.

 

[free1]

Assuming the device is digital, take two LED's, any two colours. Hook one up to TX and ground and hook the other one to RX and ground. Start your device and make it send data to the port. If one light isn't flashing on and off randomly, then try switching GND with +ve (in other words, connect the LED's to +ve) and try again. Either way, when you make your device send data to the port, one led should blink. If it doesn't, your LED is dead and u must use another LED.

The LED that goes on and off randomly is the result of the TX line.

Hi all,

may be it is help if you visit this site about rs232,

www.geocities.com/bagtool/serial_basic.html

free