Registered: Apr 2000
Location: Madison,AL
Posts: 25

Anyone had luck interfacing a Handspring to an external serial device using pins 1,4,and 8 on docking connector? I am running a Palm program (Delorme's Solus PRO) which communicates with an external GPS reciever. When I probe pin 8 (TXD) with an oscilloscope I see NO ACTIVITY on the TXD line from the Handspring. Are there any compatability issues, enable signals, etc?

Thanks!

Registered: Dec 1999
Location: Connecticut USA
Posts: 2682

For starters, Pin 2 needs to be tied to ground for the Visor to recognize serial activity. However, the docking connector does not have any handshaking lines, only RXD and TXD. Also, they are TTL signals as opposed to RS232.

Check out this thread, http://discussion.visorcentral.com/...ML/000489.html, for another reply I gave on the serial port. There are many others discussing this as well.

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MarkEagle - Ice is nice!

Registered: Apr 2000
Location: Madison,AL
Posts: 25

Thanks for the tip, but your HTML link was broken.

OK, I tried grounding pin 2 (Hot Sync int) but I still see NO DATA being sent on TXD. (Yes I realize that it is TTL).

Is it possible that the application written for the Palm is expecting a handshake signal that isn't present on the Handspring?

Does anyone know of any issues on the software side concerning PALM vs Handspring using the serial connector?

I would have bought a Palm if I had realized that the serial connector on the Handspring was TTL AND not Palm S/W compatable(I don't mind building an adapter cable).

Registered: Apr 2000
Location: Madison,AL
Posts: 25

Limited Success!
Using the Handspring Serial Docking cradle and a null modem and pulling up RTS and DTR (using HP4952 protocol analyzer), I was able to get the Handspring (running Delmorme's Solus PRO) to communicate with the Delmore Earthmate GPS receiver.

Here are the two things I discovered
1) RTS is required to be active to power the RS-232/TTL chip in the Handspring Docking Cradle.
2) DTR is required to enable the Earthmate to send data back to the Handspring.

Issue: Now I have to find a signal on the Earthmate or Cradle to pull RTS and DTR to RS-232 active levels so this will work w/o the 5k$ protocol analyzer in the path!

Registered: Dec 1999
Location: Connecticut USA
Posts: 2682

In the serial cable I built, RTS needed to be tied to CTS on the PC side in order to sync. I'm also using RTS and DTR to provide power to the transceiver chip. This is probably why other peripherals won't work... they aren't providing the necessary power at RTS/DTR.

Again, I believe the intent of Handspring was to push all this out to the Springboard instead.

Registered: Apr 2000
Location:
Posts: 73

I was having trouble getting my GPS to work with the Visor serial cradle. When I tried to initialize GPS communication by using the "start button" of Quo Vadis GPS mapping software, I lost synchronization after only 6 NMEA sentences every time - after only 5 seconds!

After some experimentation though, I was able to get the Visor/Garmin GPS 12/Quo Vadis combination working by taking apart my serial cradle and soldering a lead to the PCB connector that goes directly to pin 1 (RXD) of the Visor. I soldered another lead to the PCB connector that goes directly to pin 4 (ground) of the Visor.

The GPS communication and autoscrolling works perfectly if I do the following connection sequence:

1. Directly connect pin 1 (RXD) and pin 4 (GND) to the GPS 12 via the above soldered leads and initialize my Visor GPS software (i.e., tap "start" in the GPS window of Quo Vadis)

2. then disconnect the directly connected pins 1 and 2, and then reconnect the Visor serial cable to the GPS 12.


The GPS 12/Visor/Quo Vadis then works perfectly. The messages window scrolls continuously with NMEA messages and never stops and the auto scrolling mapping function scrolls perfectly along with your GPS position as you change position.

Step one above must somehow "synchronize the frame" (maybe with a sync pulse or handshake?)in order for continuous NMEA communication with the GPS.

By the way, I tried several other software package demos (i.e., Atlas, Placetrace, etc.) and I experienced exactly the same problem. The technique I described above worked perfectly for these programs also. I have to believe this framing problem is related to the circuitry in the cradle (it's certainly not the software). I understand that it's TTL and not RS-232, if this makes a difference.