VisorCentral.com - was the hotsync port intentionally broken??

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VisorCentral.com (http://discussion.visorcentral.com/vcforum/index.php)
- Visor & Deluxe (http://discussion.visorcentral.com/vcforum/forumdisplay.php?forumid=1)
-- was the hotsync port intentionally broken?? (http://discussion.visorcentral.com/vcforum/showthread.php?threadid=11831)

Posted by laird on 02-14-2001 05:10 AM:

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

Posted by EricG on 02-14-2001 05:55 AM:

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Posted by RoofusPennymore on 02-14-2001 07:37 PM:

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?

Posted by EricG on 02-14-2001 09:16 PM:

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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Posted by miradu on 02-14-2001 09:42 PM:

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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Posted by laird on 02-14-2001 10:18 PM:

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.

Posted by miradu on 02-14-2001 11:24 PM:

link's bad..

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Posted by EricG on 02-14-2001 11:40 PM:

quote:
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.

USB doesn't use flow control.. The "serial" in Universal Serial Bus (USB) isn't the same serial you are thinking about.. Thats why there is no flow control and the voltages are TTL... Read up on the USB specifications..

Handspring correctly implemented the USB port..

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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

Posted by laird on 02-14-2001 11:56 PM:

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

Posted by RoofusPennymore on 02-15-2001 12:10 AM:

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.

Posted by MarkEagle on 02-15-2001 12:15 AM:

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

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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Posted by EricG on 02-15-2001 03:34 AM:

quote:
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

Thats EXACTLY what USB is.. Don't treat it like an RS-232 serial port as IT IS NOT... It's USB, USB calls for TTL level voltages.. so it's not broken it's designed according to the USB specifications, not the RS-232 specs.. I think you are not really getting it.. USB uses similar and somewhat related technology as (rs-232) serial but it was never designed to be "compatible" with RS-232, that's kinda a happy coincidence. The RXD and TXD lines you see are USB RTX and USB TXD not RS-232, don't get confused by this... With some software tricks you can force a USB connection to act "like" (and I put the word, like, in quotes) an RS-232 connection, but understand that this is "like" and not "exactly the same as". USB uses those RXD and TXD lines to function.

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Posted by MarkEagle on 02-15-2001 10:51 PM:

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

USB is not TTL level. USB has a spec of +5/-5 while TTL is 3 or less (me thinks). USB is also provides a power interface in addition to its data signals.

What's important to remember here is that the Visor has both USB and serial on its connector. Pins 5 and 6 are the USB data signals while 1 and 8 are the serial (at TTL voltage levels). I think laird is only referring to the serial portion of the interface, which is broken when compared to that of the Palm due to the lack of control signals.

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Posted by laird on 02-16-2001 01:51 AM:

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

I don't think you are correct on this. This image: http://www.area.com/laird/visor/usb.jpg shows pinouts for standard USB ports.

From a USB faq:
A differential "1" is defined as (D+) - (D-) > 200 mV and a "0" is defined as (D+) - (D-) The line encoding used is always NRZI.

My understanding of USB is that it is two wire differential serial just like rs-232 except the encoding is different, the pairs are twisted, and there's sheilding.

Here's another image from the devkit that makes it really clear: http://www.area.com/laird/visor/visor-serial-2.jpg

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

Posted by EricG on 02-16-2001 04:39 AM:

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

Posted by zelchenko on 02-16-2001 04:49 AM:

a little hazy, ask again

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

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

Posted by potter on 02-16-2001 04:15 PM:

quote:
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

There is a charge pump between the batteries and Vcc. Thus unless the batteries are deadly low, Vcc is held at 3.3 volts.

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