A usb HID virtual keyboard communication interface in a measuring instrument
A technology of communication interface and virtual keyboard is applied in the field of communication interface to achieve the effect of saving financial resources and labor costs
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[0021] The specific implementation is as follows:
[0022] figure 2 , the model of the CPU is LPC2478. LPC2478 is a wide range of highly integrated microcontrollers, LPC2478 integrated USBdevicecontroller function. The pins provided by the CPU to the external USB interface are USB_D+1 and USB_D-1. R1 and R2 are USB data line protection resistors, and C1 and C2 are filter capacitors. R3 is a pull-up resistor. When the USB device is connected to the host computer, it will make the signal level of the USB_D+ line of the host computer become high, and let the host computer know that there is a USB device inserted. The lightning arrester U plays a protective role and controls the voltage on the data line within a reasonable range.
[0023] When the USBdevice interface of the test instrument is connected to the computer through a USB cable, the signal level of the USB_D+ line of the computer host becomes high, and the computer host starts to enumerate the USBdevice interface. ...
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