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-rw-r--r--cores/arduino/USBCore.cpp4
1 files changed, 4 insertions, 0 deletions
diff --git a/cores/arduino/USBCore.cpp b/cores/arduino/USBCore.cpp
index 8bcf66c..decfd6b 100644
--- a/cores/arduino/USBCore.cpp
+++ b/cores/arduino/USBCore.cpp
@@ -638,7 +638,11 @@ void USBDevice_::attach()
_usbConfiguration = 0;
UHWCON = 0x01; // power internal reg
USBCON = (1<<USBE)|(1<<FRZCLK); // clock frozen, usb enabled
+#if F_CPU == 16000000UL
PLLCSR = 0x12; // Need 16 MHz xtal
+#elif F_CPU == 8000000UL
+ PLLCSR = 0x02; // Need 8 MHz xtal
+#endif
while (!(PLLCSR & (1<<PLOCK))) // wait for lock pll
;