LPC1800 VBUS Pin

[peter_furtner]

My customer is using the LPC1800 for a USB application. Now they want to use the VBUS Pin of the USB1 Interface to discover Connect/Disconnect conditions. How is this done?

Regards,

Peter .

[ericding]

Hi Peter,

Could you explain more of this application?

Is LPC1800 used as a USB host or device?

It's the device's responsibility to actively connect to the host, and host may need to provide power to the device via VBUS pin.

[peter_furtner]

Hi Eric,

the LPC1800 USB1 Interface is used as USB-Device.

The customer wants to discover the case that the USB gets disconneted from the host (i.e. the USB-Cable gets unplugged)

In this case the VBUS Signal on the pin gets LOW (because of the external Pull-Down). But the customer doesn't know, which bit in any of the internal Registers to read to discover this case.

Thanks,

Peter

[ericding]

Hi Peter,

Below descriptions may give you some hint.

[peter_furtner]

Hi Eric,

the message also says “REMARK: The setting of this bit has no effect if the USB1_VBUS function of P2_5 is enabled through the SFSP2_5 register.“

The customer did enable the USB1_VBUS Signal through SFSP2_5. Otherwise he would not get the external signal into the device.

Still, the question is: How can he read the status of the external VBUS Signal in the device.

Regards,

Peter

[ericding]

Hi Peter,

My understanding of the remark is that writing/setting has no effect, not necessarily means reading. 

Because VBUS is an input signal, not like general I/O.

May be you can test and verify it with a board.

[bernhardfink]

Hi Peter,

P2_5 is an input to the USB1 full speed transceiver which works as a VBUS power detector. This sensing input is then automatically controlling the internal vbus_valid signal.

In case you don't use this transceiver input at pin P2_5, you could use any other GPIO or an ADC input to sense the VBUS signal level. By means of polling or with a level triggered interrupt you can then write by software into the bit USB_VBUS and control the internal signal vbus_valid by software.

Regards,

Bernhard.

[ericding]

Hi Bernhard,

Thanks for your detailed clarification.