diff --git a/README.md b/README.md
index eaa866a..81dbbc1 100644
--- a/README.md
+++ b/README.md
@@ -45,6 +45,8 @@ WiFi+bluetooth: placeholder for ESP-32 (JTAG and serial over WiFi possible)
 
 Power: 3 Switching voltage regulators: 1.2V, 2.5V, 3.3V
 
+Clock: 25 MHz onboard, external differential clock input
+
 Low power sleep: RTC clock wakeup, quartz and battery