Lantronix DSTni-EX Benutzerhandbuch

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USB uses pull-up or pull-down resistors to determine when an attach or detach event occurs on 
the bus. Host mode complicates the resistors, since it requires devices to operate as either a 
USB target device or a USB host. Figure 4-5 shows the two resistor combinations required for 
USB targets and hosts. 

Normally, the USB operates in normal mode with HOST_MODE_EN=0. This mode enables 
resistor R1 and disables the R2 resistors. When the device connects to a PC host, the host 
recognizes that DPLUS is pulled up, indicating that a full-speed device is attached. 

When the device is in host mode (HOST_MODE_EN=1), the R2 resistors are enabled and the 
R1 resistor is disabled. When a USB target connects to the USB, the R1 in the target causes 
the DPLUS signal (or DMINUS for a low-speed device) to go HIGH, activating the ATTACH 
interrupt.