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USB to Serial Port cable for 41CL
08-28-2016, 05:31 AM
Post: #1
USB to Serial Port cable for 41CL
Hi everyone,

I'm about ready to connect my 41CL to a PC, but wasn't certain about using a Sabrent USB to DB9 serial port adapter cable for the task. A Google search of MoHPC didn't turn up any mention of using a USB adapter cable. I usually like to ask "Do you think [setting myself on fire/drinking Clorox/jumping off a bridge] is a dumb idea?" before embarking on something like this I haven't tried before.

On my 41CL I have the serial port accessory for the 41CL and the DB9 to audio plug cable provided for the port cover receptacle. I picked up a Sabrent adapter cable at Frys long ago to communicate with an HP48 via its DB9 serial port adapter cable; works just fine. A quick check of the DB9 pins shows about 6.5V on some of them (scary!). The 41CL manual mentions an RS232 transceiver, and the schematics show a part with such a label but alas no part number to look up the data sheet. Having used USB to 3.3/5V serial port adapters for Arduino type targets, I want to be sure I'm not applying an inappropriate voltage to the 41CL board.

I'm posting the question here in part so that others can get a quick answer in the future. But of course I'm also asking the more pertinent question, do you think [setting myself on fire/drinking Clorox/plugging my 41CL into a (Sabrent/other) USB to DB9 adapter] is a good idea?

Should work, yeah?
~ Mark
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08-28-2016, 11:31 AM (This post was last modified: 08-28-2016 11:31 AM by Ángel Martin.)
Post: #2
RE: USB to Serial Port cable for 41CL
I wouldn't know about the fire/clorox/bridge - but the USB/Serial cable seems like a safe move to me. I've used one of those for a while for my laptop, which doesn't have a serial port - without any glitches. Mind you, there might be fundamental differences between those cable adapters, but I wouldn't think bad enough to damage your CL...

For the authoritative answer wait for Monte's response of course.
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08-28-2016, 12:48 PM
Post: #3
RE: USB to Serial Port cable for 41CL
As Angel noted, Monte is the source for advice about possible damage due to voltage levels, though I suspect it's OK.

But I suggest you test to verify basic connection with a real serial port first (assuming you have access), as a frequent problem, which appears to be cable failure, is the internal serial connector simply not being tight enough. This happened to me and several other folks, and can easily happen.

This will verify the cable installation, so you don't waste time troubleshooting the USB connection if it's really just a loose internal connection.

Have fun with the 41CL !

--Bob Prosperi
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08-28-2016, 02:47 PM
Post: #4
RE: USB to Serial Port cable for 41CL
I do not have a physical serial port on my Mac computers (Mini/Pro/BookPro/...).
I have been using USB-to-Serial adapters for years without any problems.
What is important is the USB chip used inside the converter.
All USB-to-Serial adapters uses chips from these manufacturers:
    Most popular
  • Future Technology Devices International (FTDI) (drivers)
  • Prolific (drivers)

    Less popular
  • Slicon Labs (drivers)
  • ...
Note: some FTDI chips have been cloned and some FTDI drivers bricked them but I do not think it is still the case.

Sylvain
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08-29-2016, 06:04 PM
Post: #5
RE: USB to Serial Port cable for 41CL
(08-28-2016 05:31 AM)mfleming Wrote:  On my 41CL I have the serial port accessory for the 41CL and the DB9 to audio plug cable provided for the port cover receptacle. I picked up a Sabrent adapter cable at Frys long ago to communicate with an HP48 via its DB9 serial port adapter cable; works just fine. A quick check of the DB9 pins shows about 6.5V on some of them (scary!). The 41CL manual mentions an RS232 transceiver, and the schematics show a part with such a label but alas no part number to look up the data sheet. Having used USB to 3.3/5V serial port adapters for Arduino type targets, I want to be sure I'm not applying an inappropriate voltage to the 41CL board.

The 41CL serial port is RS232. That means the standard voltage levels.
The driver is a Maxim MAX3221.
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