diff --git a/lib/mcp23008-17.js b/lib/mcp23008-17.js
index 059c383..9de3d34 100644
--- a/lib/mcp23008-17.js
+++ b/lib/mcp23008-17.js
@@ -35,7 +35,7 @@ class MCP23008 extends Device {
   }
 
   pin(id) { return this.ports.A.pin(id) } // get a reference to a particular pin's object
-  pid(address) { return this.ports.A.pid(address) }
+  pid(address) { return this.ports.A.pid(address) } // return pin id for a given address on a port
 
   inter(port = 'A') {
     return this.ports[port].interrupt