VBUS disable on LPC55s36

[madhubanti]

Hi

I am using lpc55s36. In my circuit diagram the vbus pin is not connected and kept open. The problem is i am not being able to detect my ebedded device on the port list on my laptop when i connect through USB.

Is there anyway I can remove the VBUS detection related code, so that I can access the port on my laptop and communicate through PUTTY to my embedded device.

I went through the code of the SDK example of  lpcxpresso55s36usb_dev_cdc_vcom_lite_bm.

[Alice_Yang]

Hello @madhubanti 

Sorry, there is no code to remove the VBUS detection. The device needs to check the VBUS voltage.

BR

Alice

[madhubanti]

My circuit has the following connection 

As you can see the USB0_3V3 pin is connected to a voltage. but the PIO1_31 pin which the USB_VBUS pin has been kept disconnected. Will this setup not work since the VDD pin is connected always to a source. 

Also we had the same circuit implementation for another device, but it uses zephyr os and it works without the PIO1_31 pin being connected.

Can you give us some insight into how this is not working for bare metal implementation of the SDK code but working when implemented with zephyr.

[Alice_Yang · Accepted solution]

Hello @madhubanti 

For the 0A revision of the device, the VBUS voltage is not checked. Thus, the USB_VBUS can remain disconnected. However, this detection feature was implemented in the 1B devices. In the 1B devices, PIO1_31 should be connected to VBUS. You can refer to the schematic of the LPCXpresso5536 - evb. On this schematic, for the 1B version devices, connect pins 1 - 2 of JP46.

 

BR

Alice

 

[madhubanti]

Thank you for the clarification!  The circuit design on the EVK board is such that you cannot ignore the PIO1_31 pin.

But if we want to use the sdk example code of vcom_cdc_lite_bm for the usb driver code in our codebase for our device then, where on the firmware side is this check being done? Which file or variable to look for? 

I couldn't find on the firmware side so far. For the device we are building, it uses LPC55s36 MCU. Hence, if we could get to know where the vbus detection is taking place we can customize that part of code in the firmware for our device.

Looking forward to your response!

Best

Madhubanti

[Alice_Yang]

Hello @madhubanti 

Thank you for your reply.

There's no code to check as it's not controlled by code. This is a hardware behavior.

BR

Alice

[madhubanti]

Also i am using USBFS pins.