Can I program my device using the “Do not use (DNU)” USBIO pins? - KBA233972
Community Translation: 使用禁止（DNU）” USBIOピンを使用してデバイスをプログラム出来ますか？ - KBA233972
PSoC™ 3 and PSoC™ 5LP MCU devices have USBIO pins even if they do not support the USB functionality. For example, CY8C3666LTI-027 supports the USB functionality, while CY8C3666LTI-201 does not. However, both these devices have USBIO pins.
If the device supports the USB functionality, you can use these pins either for limited digital functionality and device programming or as a USB interface. See the respective device to learn about supported functionalities for these pins.
If the device does not support the USB functionality, programming with these pins must not be attempted even if the pinout diagram shows USBIO pins. Figure 1 is an image taken from the PSoC™ 3 device datasheet that shows USBIO pins.
The note below the pinout diagram in the datasheet (Note ) reads thus: Pins are Do Not Use (DNU) on devices without USB. The pin must be left floating. This implies that although the USB / SWD pins are present in the devices without USB support, SWD programming using P15 and P15 pins is not supported.