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I'm no means an expert but up to USB 2.0 there were 4 pins (2 for power and 2 differential signals for bidirectional data) With USB 3.0 they added 4 more signal
by pkaye 8y ago
I'm no means an expert but up to USB 2.0 there were 4 pins (2 for power and 2 differential signals for bidirectional data) With USB 3.0 they added 4 more signals for separate transmit/receive. Initially they used 8b/10b encoding and then switched to 128b/132b encoding. They also increased the signaling rate with each generation. Also in the USB 2.0 and earlier the higher level protocols were kind of inefficient with lots of back and forth. So they improved upon that. And I'm sure they also tightened up on the cable and connection specs to increase the signaling rates. So a lot of little improvements added up.
- chrisseaton 8y ago> With USB 3.0 they added 4 more signals for separate transmit/receive So is it not actually serial any more?
- _wmd 8y agoTransmit and receive previously shared pins, USB 3 split transmit and receive into separate pairs, which are still serial edit: yikes, looks like USB C doubled the number of those separate pairs, for a total of 6 data pins (2x RX, 2x TX, 2x USB 2.0 RX/TX)
- projektfu 8y agoIt’s better to say they were mirrored to make the connector work the same upside down, and then they expanded the spec to allow simultaneous use, effectively doubling the throughput.
- TOGoS 8y agoMultiple serial connections in parallel.
- matthewmacleod 8y agoIt's more like… multiple serial connections over the same cable – kind of like PCI-E, SATA etc.
- jotux 8y agoIt's a low-speed differential pair that negotiates the initial communication. Once the bus knows it can go to a faster speed, it will switch to a separate receive differential pair and transmit differential pair. -Power -Ground -Signal Ground -USB2 data+ -USB2 data- -USB3 RX+ -USB3 RX- -USB3 TX+ -USB3 TX- So it's a slow serial bus that negotiates traffic onto a faster serial bus. https://en.wikipedia.org/wiki/USB_3.0#Pinouts https://en.wikipedia.org/wiki/USB_3.0#Pinouts
- cesarb 8y ago> It's a low-speed differential pair that negotiates the initial communication. AFAIK, it's not, the SuperSpeed (USB3) wires have their own independent negotiation; the device switches to the USB2 wires only when USB3 is not detected. This also explains how the proposed VirtualLink alternate mode can have USB3 without the USB2 pair.
- silotis 8y agoSerial/Parallel have commonly accepted technical meanings in the context of data interfaces which aren't necessarily intuitive. Parallel refers to taking a raw bit stream and sending N bits at a time down N wires to a receiver who reads N bits at a time and reconstructs the bitstream. This was a common technique in the early days of computing because it is very simple to implement and low clock speeds meant it was often the only practical way of increasing the throughput of an interface. As clock speeds increased, keeping each of the N signals in sync became increasingly difficult. This eventually lead to parallel interfaces falling out of favor and serial interfaces becoming dominant. The defining characteristic of a serial interface is that the data signal itself also serves as the clock signal which keeps sender and receiver in sync. Modern "parallel serial" interfaces like USB 3 consist of multiple serial links which are multiplexed using a framing protocol of some sort. So from a signaling standpoint they are still considered serial interfaces, even though data is in fact being sent in parallel.
- kanox 8y agoThanks! I don't know much about hardware design issues and this is a very readable explanation.
- zepearl 8y agoGreat explanation - thanks!
- gameshot911 8y agoAwesome comment.