diff --git a/rtu/config.lua b/rtu/config.lua
new file mode 100644
index 0000000..39b23ad
--- /dev/null
+++ b/rtu/config.lua
@@ -0,0 +1,10 @@
+RTU__DEVICES = {
+    {
+        name = "boiler_0",
+        reactor_owner = 1
+    },
+    {
+        name = "turbine_0",
+        reactor_owner = 1
+    }
+}
diff --git a/rtu/rtu.lua b/rtu/rtu.lua
new file mode 100644
index 0000000..97e11f7
--- /dev/null
+++ b/rtu/rtu.lua
@@ -0,0 +1,78 @@
+function rtu_init()
+    local self = {
+        discrete_inputs = {},
+        coils = {},
+        input_regs = {},
+        holding_regs = {}
+    }
+
+    local count_io = function ()
+        return #self.discrete_inputs, #self.coils, #self.input_regs, #self.holding_regs
+    end
+
+    -- discrete inputs: single bit read-only
+
+    local connect_di = function (f)
+        table.insert(self.discrete_inputs, f)
+        return #self.discrete_inputs
+    end
+
+    local read_di = function (di_addr)
+        return self.discrete_inputs[di_addr]()
+    end
+
+    -- coils: single bit read-write
+
+    local connect_coil = function (f_read, f_write)
+        table.insert(self.coils, { read = f_read, write = f_write })
+        return #self.coils
+    end
+
+    local read_coil = function (coil_addr)
+        return self.coils[coil_addr].read()
+    end
+
+    local write_coil = function (coil_addr, value)
+        self.coils[coil_addr].write(value)
+    end
+
+    -- input registers: multi-bit read-only
+
+    local connect_input_reg = function (f)
+        table.insert(self.input_regs, f)
+        return #self.input_regs
+    end
+
+    local read_input_reg = function (reg_addr)
+        return self.coils[reg_addr]()
+    end
+
+    -- holding registers: multi-bit read-write
+
+    local connect_holding_reg = function (f_read, f_write)
+        table.insert(self.holding_regs, { read = f_read, write = f_write })
+        return #self.holding_regs
+    end
+
+    local read_holding_reg = function (reg_addr)
+        return self.coils[reg_addr].read()
+    end
+
+    local write_holding_reg = function (reg_addr, value)
+        self.coils[reg_addr].write(value)
+    end
+
+    return {
+        count_io = count_io,
+        connect_di = connect_di,
+        read_di = read_di,
+        connect_coil = connect_coil,
+        read_coil = read_coil,
+        write_coil = write_coil,
+        connect_input_reg = connect_input_reg,
+        read_input_reg = read_input_reg,
+        connect_holding_reg = connect_holding_reg,
+        read_holding_reg = read_holding_reg,
+        write_holding_reg = write_holding_reg
+    }
+end
diff --git a/rtu/startup.lua b/rtu/startup.lua
new file mode 100644
index 0000000..de9a784
--- /dev/null
+++ b/rtu/startup.lua
@@ -0,0 +1,6 @@
+--
+-- RTU: Remote Terminal Unit
+--
+
+os.loadAPI("config.lua")
+os.loadAPI("rtu.lua")
diff --git a/scada-common/modbus.lua b/scada-common/modbus.lua
new file mode 100644
index 0000000..1e47f9c
--- /dev/null
+++ b/scada-common/modbus.lua
@@ -0,0 +1,14 @@
+function modbus_init(rtu_dev)
+    local self = {
+        rtu = rtu_dev
+    }
+
+    function _1_read_coils(c_channel_start, count)
+    end
+
+    function _2_read_discrete_inputs(di_channel_start, count)
+    end
+
+    function _3_read_multiple_holding_registers(hr_channel_start, count)
+    end
+end