diff --git a/ustc3.json b/ustc3.json
index 8ef377e..412ce8a 100644
--- a/ustc3.json
+++ b/ustc3.json
@@ -4,6 +4,7 @@
     "hw_rev": "v1.1",
     "base": "standalone",
     "core_addr": "192.168.1.75",
+    "ext_ref_frequency": 10e6,
     "peripherals": [
         {
             "type": "dio",