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50g "RS232" port - Printable Version

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50g "RS232" port - James M. Prange (Michigan) - 08-04-2006

From what I've read on comp.sys.hp48, the 50g's "RS232 port" is a
"serial port", but really not RS-232, so don't expect to connect
it to real RS-232 devices out of the box.

It uses a "4-pin mini-B" connector, with ground, RX, TX, and
battery voltage (+6V nominal) pins. The RX and TX pins use TTL
(3.3V) signal levels, so you'll need a level-shifter to use it
with real RS-232 devices. The battery voltage at the port seems an
obvious power source for a level-shifter, or for that matter,
anything else you want to use it for. Note that all of this seems
to be undocumented by HP so far.

HP isn't offering the required cable and level-shifter even as an
optional accessory, and at last report, has no intention of doing
so, although it might ask Samson Cables about supplying one. For
now, we're on our own when it comes to actually using this serial
port. To be sure, building a cable and level-shifter to allow the
50g to be used with RS-232 devices shouldn't be difficult, but I'd
expect HP to offer it.

Of course, the 48gII uses the same RX and TX signal levels (at its
port, not at the other end of the cable supplied with it), so
building a cable to connect a 50g to a 48gII, another 50g, or any
other device using these signal levels should be very simple.

And no, the 48gII's cable with its built-in level-shifter won't
fit the 50g. I suppose that an adapter could be made to allow
this, but note that the level-shifter in the 48gII's cable expects
to steal its power from a real RS-232 port on the other device.
For using a 48gII cable with a device that doesn't supply the
power, one could build a very simple adapter to supply power from
an external source.

Regards,
James

Edited: 4 Aug 2006, 3:12 p.m. after one or more responses were posted


Re: 50g "RS232" port - Thomas Okken - 08-04-2006

Is the 50g's serial port compatible with the one on the 48S/SX/G/GX? Maybe that cable would work...

- Thomas


Re: 50g "RS232" port - Tim Wessman - 08-04-2006

No.

Since we are targeting our products towards survyors, we have considred developing the cable. We already have some that work.

The problem for us however is this: the connector is juts TOO LOOSE to be of any real value for a surveyor. Any bit of pressure in any direction and it falls out.

TW


Re: 50g "RS232" port - James M. Prange (Michigan) - 08-04-2006

Quote:
Is the 50g's serial port compatible with the one on the 48S/SX/G/GX?

For details of the 48 series serial port, see the documents at http://www.hpcalc.org/search.php?query=I%2FO+technical+guide. Connecting a 50g's TX pin to a 48 series' RX pin might work, but I doubt that applying -3.5V from the 48 series' TX pin to the 50g's RX pin would be a good thing to do.

Since the 48 series' shield pin is connected to ground only through a capacitor, I don't suppose that connecting it to the 50g's battery pin would harm anything, but I wouldn't see any advantage to doing so either.

Quote:
Maybe that cable would work...

The connector is very different. For a picture of the ports on the 50g, see http://mikemander.servehttp.com:8008/hp/HP50g/pages/page_8.html. For pictures of plugs that should fit the "serial port", see http://www.panintl.com/CB-9B-1.htm, http://www.datapro.net/products/1597.html,
and http://www1.jaycar.com.au/productView.asp?ID=WC7720.

Actually, I think that the "4-pin mini-B" connectors are proprietary, not really USB-IF compliant.

I guess that you already know what the 48 series serial port and cable looks like.

Regards,
James

Edited: 4 Aug 2006, 3:15 p.m.


Re: 50g "RS232" port - James M. Prange (Michigan) - 08-04-2006

Quote:
No.

Agreed.
Quote:
Since we are targeting our products towards survyors, we have considred developing the cable. We already have some that work.

Excellent!
Quote:
The problem for us however is this: the connector is juts TOO LOOSE to be of any real value for a surveyor. Any bit of pressure in any direction and it falls out.

Does that seem to be the design of the "4-pin mini-B" connection? Would a male connector from a different source perhaps fit better?

Regards,
James


Re: 50g "RS232" port - Tim Wessman - 08-04-2006

I don't think it is the specific connector itself, but the design of the connector. The few we have been able to find are all the same. The connector just isn't designed to stay in tightly.

I would say the fit on the USB connector is 3-5x as snug. We don't have any money at the moment to be putting into cables that we feel won't even work for our customers. Once we've sold a few thousand data collectors however. . . ;-)

I know HP can make this cable with no trouble. They just don't seem to think there is demand for it. Charge 30$ per cable, and I'm sure those that really need it will gladly pay.

Quick search finds two things that will work for the calculator for those DIYers.

http://www.superdroidrobots.com/shop/category.asp?catid=41
http://www.tildesign.nl/rs232_ttl_converter-20107101P2N

TW


Re: 50g "RS232" port - Eric Smith - 08-04-2006

No, neither the connector nor the electrical signal levels match the 48S/SX and 48G/GX/G+.

The connector is not the same as the 48GII, but it is electrically the same.