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usb version
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usb version

by toasted_ry on Mon Jul 14, 2008 8:52 am

I'm interested in leveraging every last microsecond I can get out of the latest arduino diecimila board. Unfortunately I can't find documentation stating whether it uses usb 1.1 or usb 2.0. The older version should be less expensive and sufficiently fast for most applications, but the board supports the higher voltage from version 2.

So, does anybody know, usb version 1.1 or 2.0?
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by macegr on Mon Jul 14, 2008 3:34 pm

ALL USB devices made in recent years are USB 2.0. Remember when they changed the naming? Instead of USB 1.1 and USB 2.0, you now have just USB 2.0 Low, Full, and High speed.

The FT232R, the USB-to-serial chip on the Arduino, is a Full speed device.
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by westfw on Mon Jul 14, 2008 9:46 pm

In any case, the USB on an arduino talks to the microcontroller via a USB/Serial "bridge" chip whose maximum speed is considerably lower than even the speeds supported by USB1.1, so whether or not you have USB2.0 is a bit irrelevant.

You PROBABLY mean to ask whether the USB support is "low speed" (1.5Mb/s), "full speed" (11 Mbps), or "high speed" (2.0 only, 480Mbps). The FTDI chip is "full speed."

I'm not sure what you mean by wanting to "leverage every last microsecond", but you should probably be more worried about latency (how long from the time the arduino does serial output till the PC app sees it, or vis versa) than throughput. Unfortunately, there are fewer "marketing numbers" for that, and it's likely to be very dependent on the software stack in the PC rather than on "USB version."

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Re: usb version

by lou on Mon Jul 14, 2008 11:17 pm

toasted_ry wrote:the board supports the higher voltage from version 2.


What does this mean? Does USB 2.0 use a voltage other than 5 for power or a voltage other than 3.3 for signaling? If it does, I missed a memo.
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by toasted_ry on Tue Jul 15, 2008 2:34 am

Thanks for the info on the usb reclassification. I hadn't heard about the new names and frankly, I'm a little disappointed by them. Apparently usb 3 is to be called super-speed.

When I say "leverage every last microsecond", I'm trying to create a buffered USB to DMX512-A adapter with a single processor. Most of the processor's time needs to be spent transmitting DMX but I need to spend a separate chunk of time getting that information from a computer. If I take too long between DMX cycles the equipment receiving the DMX signal is likely to forget what it was doing. I'm not exactly the most efficient programmer so the fewer cycles spent getting the information the more I have to make mistakes in. I've never tried to control something in the four microsecond time frame.

As for the voltage difference, I had read somewhere that with usb 2.0 they boosted the supplied power up to 5v. It could have been a bad source, I've been reading a lot of different things recently.
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by westfw on Wed Jul 16, 2008 5:14 am

It's be pretty tough to do a USB->DMX512A adapter using an arduino. The ATmega168 chip it uses only has a single serial port, and you'd be wanting to use that for both the communications with the PC (via the Serial/USB bridge) and the dmx link. You'd almost certainly want to use a micro with two hardware serial ports, or a "real" USB port.

(I see the attraction; commercial USB/DMX units seem to come with quite a markup, don't they. I did find a couple interesting links for what I guess are essentially unbuffered USB/DMX interfaces:

http://www.usbdmx.com/usb_dmx_interface.html
http://www.telltronics.org/software/dmx/
http://www.enttec.com/index.php?main_me ... escription

Enjoiy)

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by mtbf0 on Wed Jul 16, 2008 7:22 am

if you really like the arduino for this, you could try wiring, which is based on the mega128 and has dual usarts, and costs about $80. the arduino is, after all, just a baby wiring board.

better yet, maybe an avr dragon board, with hardware usb and a pain in the ass 0.005" pitch connector layout. the at90usb257 on the dragon is very similar to the mega128, except one of the uasrts is replaced with a usb, (host, client, or otg), interface. i think you also lose an 8 bit timer. of course, there's no wiring support for the usb, so you'd be on your own there.

i've had a dragon for a while, but have never done anything with it, 'cuz i'm chicken. so, go ahead. make me ashamed.
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