RS232 cable in an LPT port

[Guest_imported]

Hi there,
I am a tech support guy and I am having a problem with a customers computer. Here is what happened. this customer is using our dongles(plugged into a parallel port on his Dell Latitude ) to protect a program. The system was working fine until he inadvertently plugs a RS232 cable into the dongle. I did not notice any problem on his LPT port. He can still use this dongle on another computer but not this one. Was his LPT port damagedby the RS 232 cable? Why I do not see anything wrong under devices in control panel?(he has WinNT on it)
Please advise!

 

[GrandpaCarl]

Yes, it is possible that he could have damaged the printer port on the computer without hurting the dongle by connecting an RS232 cable. On the parallel port, pin 7 is a data line, and pin 7 on the RS232 device is signal ground which is likely connected to chassis ground as well on the RS232 device. This may mean that the driver for the parallel port is trying to lift the ground to a logic 1. Not good!

GrandpaCarl

 

[edfair]

wouldn't worry about common on pin 7. The damage comes from pin 3 where -12 was applied on something that is a 0 to +5.
Parallel port reporting in device manager reflect all the internals of the chip but not the output drivers.
I would suspect that the output driver for data line 1 is blown. Ed Fair
unixstuff@juno.com
Any advice I give is my best judgement based on my interpretation of the facts you supply. Help increase my knowledge by providing some feedback, good or bad, on any advice I have given.

 

[papa70]

I know nothing about dongles but ... Why does it let you plug a rs232 cable into a parallel printer port connector?

 

[GrandpaCarl]

Dongles are a means of hardware locks on software, etc. Generally they are installed on the parallel port between the computer and the printer. Since many of the lines are pass through, the printer is supposed to work per normal. Only when the Dongle is interrogated by a lengthy bit string (possibly using one of the handshaking lines in a way that would not disturb the printer) is the dongle involved. There is a DB25S female connector on the dongle to permit the printer to be connected.

The RS232 cable normally plugging into the computer's serial port is a DB25S and/or a DB9S Female connector, so it can't be mixed up, so IBM thought when designing the PC. Unfortunately, in a world of various gender combinations of cables and gender changers, it is possible to goof. Sometimes you get away with it and sometimes you are not so lucky. Apparently numero22 was not so fortunate.

GrandpaCarl

 

[edfair]

Especially when the rest of the world used 25p as the default serial connection and IBM had to be different. Ed Fair
unixstuff@juno.com
Any advice I give is my best judgement based on my interpretation of the facts you supply. Help increase my knowledge by providing some feedback, good or bad, on any advice I have given.