diff --git a/assembler-8608.lua b/assembler-8608.lua
index 8efeacd..bcf11ad 100644
--- a/assembler-8608.lua
+++ b/assembler-8608.lua
@@ -81,16 +81,17 @@ local function mnemFromLine(line, instrs, validWords)
 	
 	return mnem, imms
 end
-local function addByte(state, val)
+local function addByte(state, val, code)
 	assert(val>=-128 and val<=255, "invalid byte "..val)
 	assert(state.memory[state.curAddr]==nil, "overwriting memory at "..state.curAddr)
 	state.memory[state.curAddr] = val%256
+	if code then state.codeMap[state.curAddr] = true end
 	state.curAddr = state.curAddr + 1
 end
-local function addWord(state, val)
+local function addWord(state, val, code)
 	assert(val>=0 and val<=65535, "invalid word "..val)
-	addByte(state, math.floor(val/256))
-	addByte(state, val%256)
+	addByte(state, math.floor(val/256), code)
+	addByte(state, val%256, code)
 end
 local function addSpace(state, len)
 	for i = 1, len do
@@ -104,17 +105,19 @@ local function assembleInstruction(line, state, instrs, validWords)
 	local opcode = instrs[mnem] or error("invalid instruction \""..line.."\" (mnem \""..mnem.."\")")
 	local writeimms = true
 	local padlen = 0
+	local isInstr
 	if type(opcode)=="function" then
 		padlen, writeimms = opcode(imms)
 		addSpace(state, padlen)
 	elseif opcode>=0 then
-		addByte(state, opcode)
+		isInstr = true
+		addByte(state, opcode, isInstr)
 	end
 	if writeimms then
 		for _, imm in ipairs(imms) do
 			if imm.val then
-				if     imm.len==1 then addByte(state, imm.val)
-				elseif imm.len==2 then addWord(state, imm.val)
+				if     imm.len==1 then addByte(state, imm.val, isInstr)
+				elseif imm.len==2 then addWord(state, imm.val, isInstr)
 				else error("invalid imm len") end
 			elseif imm.label then
 				table.insert(state.labelReplacements, {
@@ -122,6 +125,7 @@ local function assembleInstruction(line, state, instrs, validWords)
 					addr = state.curAddr,
 					len = imm.len,
 					rel = imm.len==1,
+					isCode = isInstr,
 				})
 				state.curAddr = state.curAddr + imm.len
 			else error("invalid imm") end
@@ -144,6 +148,7 @@ local function assembleCode(code, instrs)
 		fileName = "",
 		curAddr = 0,
 		memory = {},
+		codeMap = {},
 		labelReplacements = {},
 		labelAddrs = {},
 	}
@@ -167,12 +172,12 @@ local function assembleCode(code, instrs)
 	for _, rep in ipairs(state.labelReplacements) do
 		local labelAddr = state.labelAddrs[rep.name] or error("no label named "..rep.name)
 		state.curAddr = rep.addr
-		if     rep.len==1 then addByte(state, labelAddr-(rep.addr+1))
-		elseif rep.len==2 then addWord(state, labelAddr)
+		if     rep.len==1 then addByte(state, labelAddr-(rep.addr+1), rep.isCode)
+		elseif rep.len==2 then addWord(state, labelAddr             , rep.isCode)
 		else error("invalid labelreplace len") end
 	end
 	
-	return state.memory
+	return state.memory, state.codeMap
 end
 
 local function readFile(fn)
@@ -436,8 +441,8 @@ local function assembleFile(fn, arch)
 	code = preprocessCode(code)
 	code = fixCode(code)
 	local instrs = instrsFromArch(arch)
-	local mem = assembleCode(code, instrs)
-	return mem
+	local mem, code = assembleCode(code, instrs)
+	return mem, code
 end
 
 local function mnemsFromArch(arch)
@@ -449,7 +454,7 @@ local function mnemsFromArch(arch)
 	end
 	return mnems
 end
-local function disassembleMemory(mem, arch)
+local function disassembleMemory(mem, code, arch)
 	print("Disassembly:")
 	local mnems = mnemsFromArch(arch)
 	local addr = 0
@@ -457,7 +462,7 @@ local function disassembleMemory(mem, arch)
 	local lastaddr = 0
 	while addr<=0xFFFF do
 		local opcode = nextByte()
-		if opcode then
+		if opcode and ((not code) or code[addr-1]) then
 			local line = {}
 			local mnem = mnems[opcode] or "???"
 			table.insert(line, trim(mnem:gsub("imm[0-9]+", "")))
@@ -593,12 +598,12 @@ end
 local function strtovec(str) local v = {}; for word in str:gmatch("[^ \t\r\n]+") do table.insert(v, tonumber(word)) end; return v; end
 function AssembleFile(fn, romsizes, offsets, lens) local offset = tonumber(offsets); local len = tonumber(lens); local romsize = strtovec(romsizes);
 	local arch = arch8608
-	local mem = assembleFile(fn, arch)
+	local mem, code = assembleFile(fn, arch)
 	print(""..fn:match("[^/\\]+$").."\n")
 	printMemory(mem)
 	assert(#romsize==3, "incorrect rom size")
 	buildMemory(mem, romsize, offset, len)
-	disassembleMemory(mem, arch)
+	disassembleMemory(mem, code, arch)
 end
 ts.eval [[
 	function AssembleFile(%fn, %romsize, %offset, %len) { luacall("AssembleFile", strReplace(%fn, "$", "Add-ons/_misc/rom/8608programs/"), %romsize, %offset, %len); }