Hardware Reference
In-Depth Information
Figure 2.18
USB data signal levels
Figure 2.19
Pull-up and pull-down resistors in a USB interface
on the D
+
and D
−
must be within the ranges shown in Figure 2.18. Note also
that the terminating voltage (logic high) should be within the range 3.0-3.5 V.
Detection of device connection is accomplished by means of pull-up and
pull-down resistors placed, respectively at the input or output of a port. USB
pull-down resistors normally have a value of 15 k
whilst pull-up resistors have
a value of 1.5 k
, as shown in Figure 2.19.
