diff --git a/artiq/examples/kasli_sysu/device_db.py b/artiq/examples/kasli_sysu/device_db.py
index 1539994a9..bd1de2c82 100644
--- a/artiq/examples/kasli_sysu/device_db.py
+++ b/artiq/examples/kasli_sysu/device_db.py
@@ -42,7 +42,7 @@ for i in range(40):
     device_db["ttl" + str(i)] = {
         "type": "local",
         "module": "artiq.coredevice.ttl",
-        "class": "TTLInOut",
+        "class": "TTLInOut" if i < 4 else "TTLOut",
         "arguments": {"channel": i},
     }