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USB low-full-high speed peripherals Forum Discussions

flammmable
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The Microsoft article "USB serial driver (Usbser.sys)" tells that:

>>If you want to load Usbser.sys automatically, set the class code to 02 and subclass code to 02 in the Device Descriptor.

If I program a STM32 MCU with a CDC example with 02 class code (CDC) and 02 subclass code (ACM), the usbser.sys loads. And this makeshift USB-UART bridge detected as "Ports (COM and LPT)/COM5". If I use some USB-UART bridge IC (like FT232), commonly it's class is "Vendor specific" and they need a vendors driver. If the vendor driver has install this devices are also detected as "Ports (COM and LPT)/COMx"

The Cypress USB-UART bridge CY7C65213 has 02/02 class/subclass in the descriptor. But without the Cypress driver, this IC detected as "Other devices/Virtual Serial Port Device 00".

Actually, I can install the Cypress driver, this IC will detected as COMx and my soft will work well.

But I want to understand why the usbser.sys driver is not loading with this device? How can the Wondows understand that some USB CDC-ACM devices need the usbser.sys and the other don't need this driver? Is the difference in the descriptor or somwehere else? What instruments shall I use to spot the difference and to tell one devices from other?

 

 

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MallikaK_22
Moderator
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250 solutions authored 500 replies posted 250 replies posted

Hi,

Yes, when a Cypress device is connected it automatically binds to Cypress CDC driver. The differences between Cypress CDC driver and Microsoft CDC driver are listed here in this KBA .

You may refer to this KBA for binding the USB serial device to Microsoft CDC driver.

Regards,

Mallika

 

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MallikaK_22
Moderator
Moderator
Moderator
250 solutions authored 500 replies posted 250 replies posted

Hi,

Yes, when a Cypress device is connected it automatically binds to Cypress CDC driver. The differences between Cypress CDC driver and Microsoft CDC driver are listed here in this KBA .

You may refer to this KBA for binding the USB serial device to Microsoft CDC driver.

Regards,

Mallika