diff --git a/libraries/AP_HAL_ChibiOS/hwdef/F4BY_F427/hwdef.dat b/libraries/AP_HAL_ChibiOS/hwdef/F4BY_F427/hwdef.dat
index 990129741e5201..55a6b95b2faf33 100644
--- a/libraries/AP_HAL_ChibiOS/hwdef/F4BY_F427/hwdef.dat
+++ b/libraries/AP_HAL_ChibiOS/hwdef/F4BY_F427/hwdef.dat
@@ -128,7 +128,7 @@ PD12 TIM4_CH1 TIM4 PWM(10) GPIO(59)
 PD15 TIM4_CH4 TIM4 PWM(11) GPIO(60)
 PD14 TIM4_CH3 TIM4 PWM(12) GPIO(61)
 
-# also USART6_RX for serial RC
+# also USART6_RX for unidirectional RC,including PPM
 PC7 TIM8_CH2 TIM8 RCININT PULLDOWN LOW DMA_CH0
 # PC6 TIM8_CH1 TIM8 RCININT PULLDOWN LOW DMA_CH0