diff --git a/sw/airborne/arch/lpc21/peripherals/max1168_arch.c b/sw/airborne/arch/lpc21/peripherals/max1168_arch.c
index 14a45313da..060fafcde8 100644
--- a/sw/airborne/arch/lpc21/peripherals/max1168_arch.c
+++ b/sw/airborne/arch/lpc21/peripherals/max1168_arch.c
@@ -59,6 +59,7 @@ void max1168_read( void ) {
   SSP_DisableRti();
   SSP_Enable();
   /* write control byte - wait EOC on extint */
+  /* use internal reference and clock, sequentially scan channels 0-7 */
   SSPDR = (1 << 0 | 1 << 3 | 7 << 5) << 8;
   max1168_status = STA_MAX1168_SENDING_REQ;
 
diff --git a/sw/airborne/arch/stm32/peripherals/max1168_arch.c b/sw/airborne/arch/stm32/peripherals/max1168_arch.c
index f39881bc80..3239a3ad86 100644
--- a/sw/airborne/arch/stm32/peripherals/max1168_arch.c
+++ b/sw/airborne/arch/stm32/peripherals/max1168_arch.c
@@ -97,6 +97,7 @@ void max1168_read( void ) {
   Max1168Select();
 
   /* write control byte - wait EOC on extint */
+  /* use internal reference and clock, sequentially scan channels 0-7 */
   const uint16_t ctl_byte = (1 << 0 | 1 << 3 | 7 << 5) << 8;
   SPI_I2S_SendData(SPI2, ctl_byte);
   max1168_status = STA_MAX1168_SENDING_REQ;