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USB>SERIAL Cable with Prolific Chip
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cauer29



Joined: 03 Feb 2010
Posts: 235

PostPosted: Thu Jun 26, 2014 10:27 am    Post subject: Reply with quote

Tiku wrote:
yes i have the batteries in the remote,i have checked volts using realterm,

RTS(7) volts showing +5V when i click on Clear it shows -5v
same with TXD(3) when click on Clear Break volts drops down -5v and when pressed Set Break its showing +5v


I think that since you're seeing +/- 5V on the TXD line, this is not a logic level convertor. Usually a full RS232 level device would drive to +/-12V levels, but there are many that can only get to +/- 5V or so. That's plenty of voltage swing to work for RS232, but is not at all what is needed for a JP1 interface. Aside from the voltage levels, there is also the issue of signal inversion. Normal RS232 idles at -12V or so and drives to +12V during break. A true logic level convertor would show +5V or +3.3V at idle and go to zero volts or so during "break".


I can't say that I've ever seen a logic level USB to serial convertor with a DB9 connector. I expect that if someone did make such a thing, it would be an accident waiting to happen, as sooner or later somone will connect it to a true RS232 level device and the logic level driver/receiver will probably be damaged.
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Tiku



Joined: 11 Mar 2014
Posts: 55

PostPosted: Fri Jun 27, 2014 6:17 am    Post subject: Reply with quote

Thanks cauer29, your response is very useful, now the issue of Voltmeter's Red Probe going into -ve COM & Black Probe into +ve COM has been solved by replacing the latest driver with the driver supplied by the product manufacturer dated 31 july 07,but still some things are very confusing as instructed by 3FG
Quote:
To measure RTS, TXD, or RXD, use the volts function. Use the voltmeter to measure between GND and TXD. When SetBreak has been clicked, you should measure nearly 0 volts. When ClearBreak has been clicked, the voltage should be 3.3 or 5 volts.

According to you the TXD line should not have any volts, Right? so how come 3FG told me to measure TXD Volts.
Another thing is that in realterm when i move my cursor to TXD(3)setbreak it shows(+ve when break) and Clear Break (-ve when normal/idle), which is what at present i am getting, but you said just the opposite +5V at idle and go to zero volts or so during "break".


Now what is correct, please kindly reply.
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cauer29



Joined: 03 Feb 2010
Posts: 235

PostPosted: Fri Jun 27, 2014 9:34 am    Post subject: Reply with quote

Tiku wrote:
Thanks cauer29, your response is very useful, now the issue of Voltmeter's Red Probe going into -ve COM & Black Probe into +ve COM has been solved by replacing the latest driver with the driver supplied by the product manufacturer dated 31 july 07,but still some things are very confusing as instructed by 3FG
Quote:
To measure RTS, TXD, or RXD, use the volts function. Use the voltmeter to measure between GND and TXD. When SetBreak has been clicked, you should measure nearly 0 volts. When ClearBreak has been clicked, the voltage should be 3.3 or 5 volts.

According to you the TXD line should not have any volts, Right? so how come 3FG told me to measure TXD Volts.
Another thing is that in realterm when i move my cursor to TXD(3)setbreak it shows(+ve when break) and Clear Break (-ve when normal/idle), which is what at present i am getting, but you said just the opposite +5V at idle and go to zero volts or so during "break".

Now what is correct, please kindly reply.


I don't see any discrepancy with what 3FG told you and what I said. He told you to measure TXD while sending break and that it should be nearly 0 volts. I agree with that. When not sending break (idle), TXD should measure +3.3V or +5V. Still no difference between what I said and what 3FG is saying.

The reason that you see +5V when sending break and -5V when idle, is that your USB to serial convertor is not designed to be used for simple logic levels needed by JP1 remotes. The signal levels of +5V and -5V are not compatible with JP1 remotes. Even if it were, the signals are inverted relative to what JP1 remotes need. You can build a circuit to invert the signals and limit the voltage to 3.3V and 0V, but I see that you've already discussed that. If you build such a circuit and use it with the USB to serial convertor that you have, then it should work for your JP1 remote, assuming that your JP1 remote has not already been damaged by connecting the USB to serial convertor that you have, directly to the JP1 remote.
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