Registered: Dec 2000
Location: mountain view, ca
Posts: 36

Does anyone have any clue as to why the Visor has TTL voltages on the RXD and TXD pins?

My first assumption was that due to IC differences between the palm and visor chassis, they ran out of real-estate or made a cost/functionality assesment and decided to lose the real serial controller.

In reading the devkit in depth for more information on this subject as I try to connect my visor to my qualcomm phone, I ran across text passages that made me think that the omission of a userland functional serial port (and the lack of a serial cable from Handspring) was a religious item or else it was a design element to keep the average user from attaching any old serial device to the unit.

There are obvious reasons why this could have been the reason for the choice as it deprecates the hotsync port and pushes us to use the springboard for expansion which makes all the vendors happy of course.

Does anyone have any solid info as to why this port is broken?

Thanks,

Alan

Registered: Aug 2000
Location: Alive and well on VisorCentral.com
Posts: 861

The Visor has a real USB hotsync connector on it, not a serial one.. to use a "standard" serial connection you need extra electronics, MarkSpace makes cables that you can connect to the Visor for use with a serial device.

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Registered: Jul 2000
Location:
Posts: 61

The Visor has a real USB hotsync connector on it, not a serial one.. to use a "standard" serial connection you need extra electronics, MarkSpace makes cables that you can connect to the Visor for use with a serial device.

Really, that great! I was under the inpression that it was just a USB -> serial covertor in the cradle. Wonder if it would be possible to connect USB devices directly to the visor?

Registered: Aug 2000
Location: Alive and well on VisorCentral.com
Posts: 861

Haven't seen any yet that use it that way.. My impression was the Visor's USB was set up like that on a printer or scanner (an accessory/device), not like a PC's usb port (host/root hub).. I could be wrong ...

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Registered: May 2000
Location: St. Paul, MN
Posts: 1429

The Visor is a USB client device. USB client devices cannot control others. Handspring was very smart in using a nitve USB. Both the Clie and the Palm either use Serial or Serial->USB converters, and so you get the speed of serial or slower. The Visor uses native USB so it's FAST! in fact in my newsest PCMAG, they list the visor plat as having the fastest sync time 7 SECS! so..

(I rewrote this my typing got lost.. )

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-miradu

Registered: Dec 2000
Location: mountain view, ca
Posts: 36

The visor is a USB client and requires a master for power and arbitration. If you wanted to hack on this, you could add a single chip USB controller to a hub and have it be the master to allow things like using a USB keyboard on the visor. Lot's of hacking...

My complaint with the visor is not with the USB, it is with the voltages on the serial pins and the lack of a hardware flow control pin.

http://www.area.com/laird/visor/visor-serial-1.jpg

I'm sure they had good reasons for their signal selection on a limited number of pins but have not been able to find a narrative yet so some of the implimentation choices have me scratching my head.

Last edited by laird on 02-16-2001 at 01:52 AM

Registered: May 2000
Location: St. Paul, MN
Posts: 1429

link's bad..

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-miradu

Registered: Aug 2000
Location: Alive and well on VisorCentral.com
Posts: 861

quote:

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Originally posted by laird

My complaint with the visor is not with the USB, it is with the voltages on the serial pins and the lack of a hardware flow control pin.

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Registered: Dec 2000
Location: mountain view, ca
Posts: 36

This is not about the USB pins.

This is about the serial pins specifically RXD and TXD which are used for the serial cradle connection and keyboard and are at TTL Vcc instead of RS-232.

Please look at the image I posted.

Alan

Registered: Jul 2000
Location:
Posts: 61

The visor is a USB client and requires a master for power and arbitration. If you wanted to hack on this, you could add a single chip USB controller to a hub and have it be the master to allow things like using a USB keyboard on the visor. Lot's of hacking...

I assume you would also have to have drivers on the controler-hub or maybe the Visor.

Also, when trying to look at the link I get Access forbidden from external hosts.

Registered: Dec 1999
Location: Connecticut USA
Posts: 2682

quote:

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Originally posted by laird
Please look at the image I posted.

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The image link returns the following error message when I click on it:

Access forbidden from external hosts


I think the reason for a TTL interface was two-fold. First, it lowered the number of components and therefore the cost of the overall unit. Second, HS never really intended for the serial port to be used for anything other than syncing and keyboards. They feel (rightly so, IMHO) that Springboard technology is a better way to implement peripheral devices than the old serial method that Palm uses. The only problem with this thinking is that many of us feel the need to (and, more importantly, just want to ) be able to use standard serial devices with our beloved Visor's.

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Registered: Aug 2000
Location: Alive and well on VisorCentral.com
Posts: 861

quote:

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Originally posted by laird
This is not about the USB pins.

This is about the serial pins specifically RXD and TXD which are used for the serial cradle connection and keyboard and are at TTL Vcc instead of RS-232.

Please look at the image I posted.

Alan

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Last edited by EricG on 02-15-2001 at 03:40 AM

Registered: Dec 1999
Location: Connecticut USA
Posts: 2682

quote:

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Originally posted by EricG
It's USB, USB calls for TTL level voltages..

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Registered: Dec 2000
Location: mountain view, ca
Posts: 36

quote:

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The RXD and TXD lines you see are USB RTX and USB TXD not RS-232

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Registered: Aug 2000
Location: Alive and well on VisorCentral.com
Posts: 861

Call handspring and ask them.... maybe they can give you a definitive answer...

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"One of the most important things you learn from the internet is that there is no �them� out there. It�s just an awful lot of �us�." -- Douglas Adams

Registered: Sep 2000
Location:
Posts: 117

a little hazy, ask again

Seems laird already has it pretty clear, EricG. You may need to consult your Magic 8-Ball again.

quote:

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Originally posted by EricG
Call handspring and ask them.... maybe they can give you a definitive answer...

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Registered: Feb 2000
Location: SW Virginia
Posts: 290

quote:

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Originally posted by laird
The serial RXD and TXD lines are at TTL Vcc which means that when your batteries are running low at 2v, your serial lines RXD and TXD are also at 2v which makes it problematic

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