diff --git a/scada-common/psil.lua b/scada-common/psil.lua
new file mode 100644
index 0000000..9901e97
--- /dev/null
+++ b/scada-common/psil.lua
@@ -0,0 +1,48 @@
+--
+-- Publisher-Subscriber Interconnect Layer
+--
+
+local psil = {}
+
+-- instantiate a new PSI layer
+function psil.create()
+    local self = {
+        ic = {}
+    }
+
+    -- allocate a new interconnect field
+    ---@key string data key
+    local function alloc(key)
+        self.ic[key] = { subscribers = {}, value = 0 }
+    end
+
+    ---@class psil
+    local public = {}
+
+    -- subscribe to a data object in the interconnect
+    ---@param key string data key
+    ---@param func function function to call on change
+    function public.subscribe(key, func)
+        if self.ic[key] == nil then alloc(key) end
+        table.insert(self.ic[key].subscribers, { notify = func })
+    end
+
+    -- publish data to a given key, passing it to all subscribers if it has changed
+    ---@param key string data key
+    ---@param value any data value
+    function public.publish(key, value)
+        if self.ic[key] == nil then alloc(key) end
+
+        if self.ic[key].value ~= value then
+            for i = 1, #self.ic[key].subscribers do
+                self.ic[key].subscribers[i].notify(value)
+            end
+        end
+
+        self.ic[key].value = value
+    end
+
+    return public
+end
+
+return psil