All devices have an upstream connection to the host and all hosts have a downstream connection to link device. Upstream and downstream connectors are not mechanically interchangeable, thus eliminating illegal loopback connections at hubs such as a downstream port connected to a downstream port.
There are commonly two types of connectors, called type A Usb Resume K State type B which are shown below. Type A plugs always face upstream.
USB data flow. Full and Low speed. The K state is just the opposite polarity to the J state. A suspended device must recognise the resume signal. Version: ** Question: What are USB suspend, resume, and remote wake-up operations and how are they achieved with enCoRe™ V devices? Answer: In the. Introduction to High Speed USB. The differential state of the line is detected at the receiving the Resume is signalled by a K state for. USB in a NutShell; Introduction In high speed a ‘J’ state is a differential 1. USB transceivers will have both The device will resume operation when it. Figure 2. Suspend timing Resume signal When a device is in the suspend state, the data K state on the device port means a resume from the.
Type A sockets will typically find themselves on hosts and hubs. For example type A sockets are common on computer main boards and hubs. Type B plugs are always connected downstream and consequently type Usb Resume K State sockets are found on devices.
It is interesting to find type A to type A cables wired straight through and an array of USB gender changers in some computer stores. This is in contradiction of the Usb Resume K State specification. The only type A plug to type A plug devices are bridges which are used to connect two computers together. Other prohibited cables are USB extensions which has a plug on one end either type A or type B and a socket on the other. These cables violate the click at this page length requirements of USB.
The details on these connectors can be found in Mini-B Connector Engineering Change Notice The reasoning behind the mini connectors came from the range of miniature electronic devices such as mobile phones and organisers. The current type B connector is too large to be easily integrated into these devices. This introduces USB hosts into mobile phone and electronic organisers, and thus has included a specification for mini-A plugs, mini-A receptacles, and mini-AB receptacles.
I guess we should be inundated with mini USB cables soon and a range of mini to standard converter cables.
Standard internal wire colours are used in USB cables, making it easier to identify wires from manufacturer to manufacturer. The standard specifies various electrical parameters for the cables. It is interesting to read the detail the original USB 1. You would understand it specifying electrical attributes, but paragraph 6. We briefly address the essential points here.
As we have discussed, USB uses a differential transmission pair for data. This see more encoded using NRZI and is bit stuffed to ensure adequate transitions Usb Resume K State the data stream. The polarity of the signal is inverted depending on the speed of the bus.
USB transceivers will have both differential and single ended outputs. For example a single ended zero or SE0 can be used to signify a device reset if held for more than 10mS. Any good datasheet should specify these values and tolerances. These pull up resistors at the device end will also be used by the host or hub to detect the presence of a device connected to its port. Without a pull up resistor, USB assumes there is nothing connected to the bus.
Some devices have this resistor built into its silicon, which can be turned on and off under firmware control, others require an external resistor. When first connected to the bus, this allows the microcontroller to initialise the USB function device before it enables the pull up speed identification resistor, indicating a device is attached to the bus.
If the pull up resistor was connected to V busthen this would indicate a device has been connected to the bus as soon as the plug is inserted. Other vendors such as Cypress Semiconductor also use a programmable resistor for Re-Numeration TM purposes in their EzUSB devices where the one device can be enumerated for one function such as In field programming then be disconnected from the bus under firmware control, and enumerate as another different device, all without the user lifting an eyelid.
They are bootstraped at Usb Resume K State. You will notice we have not included speed identification for High Speed mode.
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High speed devices will start by connecting as a full speed device 1. Once it has been attached, it will do a high speed chirp during reset and establish a high speed connection if the hub supports it. If the device operates in high speed mode, then the pull up resistor is removed to balance the line.
This is also the case for a low speed USB 1. However a high speed device must not support low speed mode. It should only support full speed Usb Resume K State needed to connect first, then high speed mode if successfully negotiated Usb Resume K State.
One of the benefits of USB is bus-powered devices - devices which obtain its power from the bus and requires no external plug packs or additional cables. However many leap at this option without first considering all the necessary criteria. A USB device specifies its power consumption expressed in 2mA units in the configuration descriptor which we will examine in detail later. A device cannot increase its power consumption, greater than what it specifies during enumeration, even if it looses external power.
There are three classes of USB functions. Low power bus powered functions draw all its power from the V BUS and cannot draw any more than one unit load. The USB specification defines a unit load as mA. Low power bus powered functions must also be designed to work down to a V BUS voltage of 4. High power bus powered functions will draw all its power from the bus and cannot draw more than one unit load until it has been configured, after which it can then drain 5 unit loads mA Max read more it asked continue reading this in its descriptor.
High power bus functions must be able to be detected and enumerated at a minimum 4. When operating at a full Usb Resume K State load, a minimum V BUS of 4. Once again, these measurements are taken at the upstream plug. Should this external source fail, it must have provisions in place article source draw no more than 1 unit load from the bus.
Self powered functions are easier to design to specification as there is not so much of an issue with power consumption. This is outlined in the USB specification paragraph 7. Inrush current is contributed to the amount of capacitance on your device between V BUS and ground. The spec therefore specifies that the maximum decoupling capacitance you can have on your device is 10uF. When you disconnect the device after current is flowing through the inductive USB cable, a large flyback voltage can occur on the open end of the cable.
For the typical bus powered device, it can not drain any more than mA which is not unreasonable. So what is the complication you ask?
Suspend mode is mandatory on all devices. During suspend, additional constrains come into force. The maximum suspend current is proportional to the unit load. For a 1 unit load device default the maximum suspend current is uA. This includes current from the pull up resistors on the bus. For the purposes of power consumption, the pull down resistor at the device is in series with the 1.
Therefore this resistor sinks uA before we even start.
K-State Rec Services
Another consideration for many devices is the 3. Many of the USB devices run on 3. Linear regulators are typically quite inefficient with average quiescent currents in the order of uA, therefore more efficient and thus expensive regulators are called for. In the majority of cases, you must also slow down or stop clocks on microcontrollers to fall within the uA limit. Many developers ask in the USB Implementor's Forum, what are the complications of exceeding this limit? However in normal operation, if you try to exceed the mA or your designated permissible load, then expect the hub or source to detect this and disconnect your device, in the interest of the integrity of the bus.
Of course these design issues can be avoided if you choose to design a self powered device. Suspend currents may not be a great concern for desktop computers but with the introduction Usb Resume K State the On-The-Go Specification we will start seeing USB hosts built into mobile phones and mobile organisers.
The power consumption pulled from these devices will adversely effect the operating life of the battery.
How to issue wake-up keyboard event //Now drive the resume K-state signalling onto the USB bus. USBResumeControl = 1; // Start RESUME signaling. On 05/03/ PM, Alan Stern wrote: On Sat, 3 May , xiao jin wrote: We use usb ehci to connect with modem and run stress test on ehci. Universal-Serial-Bus the host’s downstream port must enter a high-speed K state as described in Embedded Hi-Speed Host Electrical Test Procedure. USB HW suspend resume USB 高速 high speed: USB Mbps USB 全速 full speed: USB 12Mbps USB 是用差動傳遞, Idle: J state Resume: K state.
A USB device will enter suspend when there is no activity on the bus for greater than 3. It then has a further 7ms to shutdown the device Usb Resume K State draw no more than the designated suspend current and thus must be only drawing the rated suspend current from the click 10mS after bus activity stopped.
In order to maintain connected to a suspended hub or host, the device must still provide power to its pull up speed selection resistors during suspend. USB has a start of frame packet or keep alive sent periodically on the bus. This prevents an idle bus from entering suspend mode in the absence of data.
However selected devices can be suspended by sending a command to the hub that the device is connected too.
The device will resume operation when it receives any non idle signalling. If a device has remote wakeup enabled then it may signal to the host to resume from suspend.
Another area which is often overlooked is the tolerance of the USB clocks. This is specified in the USB specification, section 7. Usb Resume K State allows resonators to be used for low cost low speed devices, but rules them out for full or high speed devices. Connectors All devices have an upstream connection to the host and all hosts have a downstream connection to the device. PCB designers will want to reference chapter 6 for standard foot prints and pinouts.
Low Speed Device with pull up resistor connected to D- You will notice we have not included speed identification read more High Speed mode.
Power V BUS One of the benefits of USB is bus-powered devices - devices which obtain its power from the bus and requires no external plug packs or additional cables.
There are three classes of USB functions, Low-power bus powered functions High-power bus powered functions Self-powered functions Low power bus powered functions draw all its power from the V BUS and cannot draw any more than one unit load. Suspend Current Suspend mode is mandatory on all devices. A high speed bus will have micro-frames sent every A full speed bus will have a frame sent down each 1. A low speed bus will have a keep alive which is a EOP End of Packet every 1ms only in the absence of any low speed data.
High speed data Usb Resume K State clocked at Full speed data is clocked at