Original Source::http://www.zytrax.com/tech/pc/serial.html
Tech Info - USB and Firewire
USB and FireWire (IEEE 1394a and b) represent the newer generations of external serial interfaces being adopted to reduce PC and connection costs and to improve performance.
USB (1.x and 2.0)
The USB specification defines A and B type connectors. A type connects to the host or a hub. Type B connects to the end peripheral. This is shown in diagram 1 below.
A new 'On-the-Go (OTG)' specification introduces a smaller (really) connector and peer-to-peer operation.
Great to see that the USB folk make their specs freely available unlike the IEEE 1394 folks.
Type A Pin assignment
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Type B Pin assignment
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Mini-USB Type A/B Pin assignment
Defined as part of the 'On-the-Go (OTG)' enhancement, features a single connector type (A/B) and peer-to-peer operation.
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IEEE 1394 (Firewire a.k.a. i.Link)
The IEEE high speed serial connector is known as Firewire and i.Link (Japan). The IEEE 1394a-1995 specification provides up to 400 M bit/sec and uses either a 6 pin connector (PCs/Computers) or a 4 pin connector (camcorders and AV equipment). The latest specification IEEE 1394b provides up to 800 M bit/sec (but is slated for 3.2 G bit/s) and uses a 9 pin connector which may operate in 'biligual mode' (will connect to either a 4 or 6 pin IEEE 1394a connectors but needs a special converter cable) or 'beta mode' (will connect to another IEEE 1394b system).
Firewire uses the Open Host Controller Interface (OHCI)
As always the lack of freely available specifications is just a pain - leading to confusion and plain stupidity. It is a shame that the IEEE 1394 working group could not take a leaf out of the IEEE 802 group which now provides specs at no cost 6 months after their initial publication. Sigh.
Firewire/i.Link 6 Pin Connector Assignment
This connector is usually found on PCs (Apple especially) and disk systems.
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Firewire/i.Link 4 Pin Connector Assignment
This very compact connector is usually found on camcorders and other digital AV equipment.
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Firewire/i.Link 9 Pin Connector Assignment
This is the new IEEE 1394b (Firewire 800) connector which allows interconnection to older 1394a systems in 'bilingual mode'(4 or 6 pin - using an appropriate converter cable). In 'beta mode' allows connection to other 1394b systems.
Note: The power specification shown below (12 - 25V) highlights the problems of keeping definitive specifications limited to folks who are prepared to shell out filthy lucre for the privilege of reading the three lines that interest them and the confusion that arises as users legitimately try to reconcile various published specs and product notes. Various device specifications, notes and descriptions contain a variety of specific power values within the range shown below. The majority of chipset specifications use a low figure of 12V, many device descriptions (some based on the same chipsets) maintain the older maximum value of 25V. Since one of the benefits of the 1394b specification is longer cable runs on certain media types we have shown the low value as 12V since this seems to allow for increased voltage drop and consequently makes sense to us. We would be delighted to provide further information and clarification on this topic if anyone cares to update us.
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