Безсистемная ошибка частотника

Дата: 07.04.2018 | Від: Deltabptawr

function as virtual COM ports. On power up or device attachment, the host computer and the device exchange information in a process called enumeration. The host requests a series of data structures called descriptors from the device. The descriptors contain information that identify the device and its intended use. The information includes the device’s Vendor ID, Product ID, Release Number and codes that identify any standard USB classes the device belongs to. During enumeration, the host also assigns a bus address to the device and requests the device to use a configuration that specifies how much current the device can draw from the bus. Assigning a Driver on the Host For each device, the host computer looks for the best match between the information in the device’s descriptors and the information in the host’s INF files or an equivalent information source for non-Windows systems . The information can be a Vendor ID/Product ID pair or USB class and subclass codes. On finding a match, the host uses the driver or drivers named in the INF file. After the device accepts the requested configuration, the host and device can begin communicating using the assigned drivers. A virtual COM-port device can use the serial.sys and usbser.sys drivers provided with Windows or an alternate driver obtained from a device vendor or other source. Some companies provide free COM-port drivers for use with the company’s USB controllers. Requirements A USB host can be a desktop or notebook computer, a handheld, or an embedded system. The host must contain host-controller hardware and must imple- 318 Inside USB ment USB protocols. To communicate with COM-port devices, the host must support the COM-port software interface and must either support the USB communication devices class or use a vendor-specific driver that implements a virtual COM port. A USB device can contain a microcontroller with an on-chip USB device controller, or the USB device controller can be on a separate chip that in prom-electric.ru

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