diff --git a/mesecons_fpga/init.lua b/mesecons_fpga/init.lua
index 941b61a..590571c 100644
--- a/mesecons_fpga/init.lua
+++ b/mesecons_fpga/init.lua
@@ -1,10 +1,10 @@
 local plg = {}
 plg.rules = {}
 
+
 local lcore = dofile(minetest.get_modpath(minetest.get_current_modname()) .. "/logic.lua")
 dofile(minetest.get_modpath(minetest.get_current_modname()) .. "/tool.lua")(plg)
 
-
 plg.register_nodes = function(template)
 	-- each loop is for one of the 4 IO ports
 	for a = 0, 1 do
@@ -180,22 +180,16 @@ plg.to_formspec_string = function(is)
 		return s .. "]"
 	end
 	local function dropdown_action(x, y, name, val)
-		local s = "dropdown[" .. tostring(x) .. "," .. tostring(y) .. ";"
-				.. "1.125,0.5;" .. name .. ";" -- the height seems to be ignored?
-		s = s .. " , AND,  OR, NOT, XOR,NAND,   =,XNOR;"
-		if val == nil then
-			return s .. "0]" -- actually selects no field at all
+		local selected = 0
+		local titles = { " " }
+		for i, data in ipairs(lcore.get_operands()) do
+			titles[i + 1] = data.fs_name
+			if val == data.gate then
+				selected = i + 1
+			end
 		end
-		local mapping = {
-			["and"] = 1,
-			["or"] = 2,
-			["not"] = 3,
-			["xor"] = 4,
-			["nand"] = 5,
-			["buf"] = 6,
-			["xnor"] = 7,
-		}
-		return s .. tostring(1 + mapping[val]) .. "]"
+		return ("dropdown[%f,%f;1.125,0.5;%s;%s;%i]"):format(
+			x, y, name, table.concat(titles, ","), selected)
 	end
 	local s = "size[9,9]"..
 		"label[3.4,-0.15;FPGA gate configuration]"..
@@ -239,20 +233,11 @@ plg.from_formspec_fields = function(fields)
 		end
 	end
 	local function read_action(s)
-		if s == nil or s == " " then
-			return nil
+		for i, data in ipairs(lcore.get_operands()) do
+			if data.fs_name == s then
+				return data.gate
+			end
 		end
-		local mapping = {
-			["AND"] = "and",
-			["OR"] = "or",
-			["NOT"] = "not",
-			["XOR"] = "xor",
-			["NAND"] = "nand",
-			["="] = "buf",
-			["XNOR"] = "xnor",
-		}
-		s = s:gsub("^%s*", "") -- remove leading spaces
-		return mapping[s]
 	end
 	local is = {}
 	for i = 1, 14 do
diff --git a/mesecons_fpga/logic.lua b/mesecons_fpga/logic.lua
index 3dca154..d9a37ef 100644
--- a/mesecons_fpga/logic.lua
+++ b/mesecons_fpga/logic.lua
@@ -1,5 +1,21 @@
+
 local lg = {}
 
+local operands = {
+	-- index: Index in formspec
+	{ gate = "and",  short = "&", fs_name = " AND", func = function(a, b) return a and b end },
+	{ gate = "or",   short = "|", fs_name = "  OR", func = function(a, b) return a or b end },
+	{ gate = "not",  short = "~", fs_name = " NOT", func = function(a, b) return not b end },
+	{ gate = "xor",  short = "^", fs_name = " XOR", func = function(a, b) return a ~= b end },
+	{ gate = "nand", short = "?", fs_name = "NAND", func = function(a, b) return not (a and b) end },
+	{ gate = "buf",  short = "_", fs_name = "   =", func = function(a, b) return b end },
+	{ gate = "xnor", short = "=", fs_name = "XNOR", func = function(a, b) return a == b end }
+}
+
+lg.get_operands = function()
+	return operands
+end
+
 -- (de)serialize
 lg.serialize = function(t)
 	local function _op(t)
@@ -11,20 +27,14 @@ lg.serialize = function(t)
 			return tostring(t.n)
 		end
 	end
-	local function _action(s)
-		if s == nil then
-			return " "
+	-- Serialize actions (gates) from eg. "and" to "&"
+	local function _action(action)
+		for i, data in ipairs(operands) do
+			if data.gate == action then
+				return data.short
+			end
 		end
-		local mapping = {
-			["and"] = "&",
-			["or"] = "|",
-			["not"] = "~",
-			["xor"] = "^",
-			["nand"] = "?", --dunno
-			["buf"] = "_",
-			["xnor"] = "=",
-		}
-		return mapping[s]
+		return " "
 	end
 
 	local s = ""
@@ -48,18 +58,14 @@ lg.deserialize = function(s)
 			return {type = "reg", n = tonumber(c)}
 		end
 	end
-	local function _action(c)
-		local mapping = {
-			["&"] = "and",
-			["|"] = "or",
-			["~"] = "not",
-			["^"] = "xor",
-			["?"] = "nand",
-			["_"] = "buf",
-			["="] = "xnor",
-			[" "] = nil,
-		}
-		return mapping[c]
+	-- Deserialize actions (gates) from eg. "&" to "and"
+	local function _action(action)
+		for i, data in ipairs(operands) do
+			if data.short == action then
+				return data.gate
+			end
+		end
+		-- nil
 	end
 
 	local ret = {}
@@ -159,21 +165,12 @@ end
 -- interpreter
 lg.interpret = function(t, a, b, c, d)
 	local function _action(s, v1, v2)
-		if s == "and" then
-			return v1 and v2
-		elseif s == "or" then
-			return v1 or v2
-		elseif s == "not" then
-			return not v2
-		elseif s == "xor" then
-			return v1 ~= v2
-		elseif s == "nand" then
-			return not (v1 and v2)
-		elseif s == "buf" then
-			return v2
-		else -- s == "xnor"
-			return v1 == v2
+		for i, data in ipairs(operands) do
+			if data.gate == s then
+				return data.func(v1, v2)
+			end
 		end
+		return false -- unknown gate
 	end
 	local function _op(t, regs, io_in)
 		if t.type == "reg" then