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What are the differences between 22.2 and 22.3?

Latest Updated:03/23/2009

Question:

The section of the USB Pin Multiplex Controller in the SH7727 hardware manual (version 4) have two Figures, 22.2 and 22.3 as the examples of transceiver connection for USB function controller (on-chip transceiver is used). What are the differences between these two figures?

Answer:

The USB specification specifies that the pull-up must be performed, only when the VBUS of the USB cable is High (or, when the VBUS is Low, the 1.5 Ω at pin D+ must not be pulled up).Therefore, the logic operation AND of the VBUS and USB1_en pin, which control the pull-up, controls the 1.5 Ω pull-up at pin D+ in Figure

22.2.The software can control the USB1_pwr_en pin without recognizing connection/disconnection of the USB cable and pull up D+ in this circuit.

On the other hand, the software must recognize that the USBF_VBUS pin becomes High by using the interrupt function, and then control the USB1_pwr_en pin and turn on the 1.5 Ω pull-up at pin D+ to meet the above USB specification in Figure 22.3.Also, it must execute the opposite processing, when the USB cable is disconnected, and turn off the 1.5 Ω pull-up at pin D+.The advantage of this circuit is to be able to reduce one external part compared to Figure 22.2, if the Low Active 3 State Buffer is used at IC2.

Suitable Products
SH7727