diff --git a/README.md b/README.md
index e542c2e..532eab5 100644
--- a/README.md
+++ b/README.md
@@ -13,16 +13,21 @@ The T400 is a 12-bit stack machine operating at 1Hz (due to ABMs only running on
 ### Instructions
 There are 8 instructions for the T400. Any values encountered by the processor that are not instructions are treated as data and pushed to the stack. While this does make both the code for the emulator and the code for the emulated computer simple, it has the downside that if you really do want the value 4095 you have to add two things together.
 
-| ins	 | function			|    mnemonic	|
-|--------|------------------------------|---------------|
-|4095	 | push program counter		| ppc		|
-|4094	 | swap TOS			| swp		|
-|4093	 | read memory from TOS		| read		|
-|4092	 | write to memory from TOS	| write		|
-|4091	 | add TOS			| add		|
-|4090	 | suptract TOS			| sub		|
-|4089	 | jump to TOS			| jmp		|
-|4088	 | skip if TOS = zero		| sez		|
+| ins	 | function					|    mnemonic	|
+|--------|----------------------------------------------|---------------|
+|4095	 | push program counter				| ppc		|
+|4094	 | swap TOS					| swp		|
+|4093	 | read memory from TOS				| read		|
+|4092	 | write to memory from TOS			| write		|
+|4091	 | add TOS					| add		|
+|4090	 | suptract TOS					| sub		|
+|4089	 | jump to TOS					| jmp		|
+|4088	 | skip if TOS = zero				| sez		|
+|4087	 | jump if TOS = zero				| jez		|
+|4086	 | jump to subroutine, push pc to retstack	| jsr		|
+|4085	 | return from subroutine, PC = top of retstack	| ret		|
+|4084	 | duplicate TOS				| dup		|
+|4083	 | drop TOS					| drop		|
 
 ## T410
 The T410, is, in essence, the write instruction in a block. You put in an address and a value and it tries to write the value to that address.
diff --git a/test3d_t400/init.lua b/test3d_t400/init.lua
index 2291c71..fe56aa9 100644
--- a/test3d_t400/init.lua
+++ b/test3d_t400/init.lua
@@ -23,7 +23,7 @@ local function push(pos,val)
  local sstring = ""
  local sstab = string.split(meta:get_string("stack"),"\n")
  sstab[#sstab+1] = tostring(tonumber(val) % 4096)
- if #sstab > 16 then
+ if #sstab > MEMSIZE then
   table.remove(sstab,1)
  end
  for k,v in ipairs(sstab) do
@@ -47,10 +47,13 @@ end
 local function t400_digiline_receive(pos, node, channel, msg)
  print("Digiline: "..tostring(pos.x)..","..tostring(pos.y)..","..tostring(pos.z).."; Channel: "..tostring(channel).."; Message: "..tostring(msg))
  local meta = minetest.get_meta(pos)
+ print(meta:get_string("state").." "..meta:get_string("waitingfor"))
  if meta:get_string("state") == "waitingdat" and meta:get_string("waitingfor") == channel then
+  print("got data")
   push(pos,tonumber(msg))
   meta:set_int("pc",meta:get_int("pc")+1)
   meta:set_string("state","running")
+  print("finished getting data")
  elseif meta:get_string("state") == "waitingins" and meta:get_string("waitingfor") == channel then
   meta:set_int("ci",tonumber(msg))
   meta:set_string("state","running")
@@ -65,6 +68,7 @@ local function t400_set_meta(pos)
   ms = ms .. "0\n"
  end
  meta:set_string("stack",ms)
+ meta:set_string("retstack",ms)
  meta:set_string("channel","Default")
  meta:set_string("state","running")
  meta:set_string("waitingfor","")
@@ -116,40 +120,83 @@ minetest.register_abm({
    local skipnext = false
    print("Attempting to run T400 node at "..pos2string(pos))
    local ci = meta:get_int("ci")
-   if ci == 4095 then
+   if ci == 4095 then -- ppc
     push(pos,meta:get_int("pc"))
-   elseif ci == 4094 then
+   elseif ci == 4094 then -- swp - why do I have this?
     local a = pop(pos)
     local b = pop(pos)
+    print("Swapping "..tostring(a).." for "..tostring(b))
     push(pos,b)
     push(pos,a)
-   elseif ci == 4093 then
+   elseif ci == 4093 then -- read
     skipnext = true
     local addr = pop(pos)
     meta:set_string("state","waitingdat")
     meta:set_string("waitingfor",meta:get_string("channel")..string.format("%X",addr))
+    meta:set_int("pc",meta:get_int("pc")+nins)
     digiline:receptor_send(pos,digiline.rules.default,meta:get_string("channel")..string.format("%X",addr),"get")
-   elseif ci == 4092 then
+    return
+   elseif ci == 4092 then -- write
     local addr = pop(pos)
     local dat = pop(pos)
     print("Writing "..tostring(dat).." to address "..addr)
     digiline:receptor_send(pos,digiline.rules.default,meta:get_string("channel")..string.format("%X",addr),dat)
-   elseif ci == 4091 then
+   elseif ci == 4091 then -- add
     print("Adding stuff")
     push(pos,pop(pos)+pop(pos))
-   elseif ci == 4090 then
+   elseif ci == 4090 then -- sub
     push(pos,pop(pos)-pop(pos))
-   elseif ci == 4089 then
+   elseif ci == 4089 then -- jmp
     local npc = pop(pos)
     print("Jumping to "..tostring(npc))
     meta:set_int("pc",npc)
-   elseif ci == 4088 then
+    nins=0
+   elseif ci == 4088 then -- sez
     local val = pop(pos)
     print(val,type(val))
     if val == 0 then
      print("Skipping because "..tostring(val).." = 0")
      nins=nins+1
     end
+   elseif ci == 4087 then -- jez
+    local addr = pop(pos)
+    local val = pop(pos)
+    if val == 0 then
+     print("Jumping to "..addr.." because "..val.." = 0")
+     meta:set_int("pc",addr)
+     nins=0
+    end
+   elseif ci == 4086 then -- jsr
+    local sstring = ""
+    local sstab = string.split(meta:get_string("retstack"),"\n")
+    sstab[#sstab+1] = tostring(tonumber(meta:get_int("pc")) % 4096)
+    if #sstab > MEMSIZE then
+     table.remove(sstab,1)
+    end
+    for k,v in ipairs(sstab) do
+     sstring = sstring .. v .. "\n"
+    end
+    meta:set_string("retstack",sstring)
+    meta:set_int("pc",pop(pos))
+    nins=0
+   elseif ci == 4085 then -- ret
+    local sstring = ""
+    local sstab = string.split(meta:get_string("retstack"),"\n")
+    local sval = tonumber(table.remove(sstab,#sstab))
+    for k,v in ipairs(sstab) do
+     sstring = sstring .. v .. "\n"
+    end
+    meta:set_string("retstack",sstring)
+    if not sval then sval = 0 end
+    meta:set_int("pc",sval)
+   elseif ci == 4084 then -- dup
+    local v = pop(pos)
+    push(pos,v)
+    push(pos,v)
+    print("Duplicating "..v)
+   elseif ci == 4083 then -- drop
+    print("Dropping stuff")
+    pop(pos)
    else
     print("Pushing "..ci.." to "..pos2string(pos))
     push(pos,ci)
diff --git a/test3d_t416/init.lua b/test3d_t416/init.lua
index 20360fa..b84d9f7 100644
--- a/test3d_t416/init.lua
+++ b/test3d_t416/init.lua
@@ -12,7 +12,7 @@ end
 print("Loading.")
 
 local function t416_digiline_receive(pos, node, channel, msg)
- print("Digiline: "..tostring(pos.x)..","..tostring(pos.y)..","..tostring(pos.z).."; Channel: "..tostring(channel).."; Message: "..tostring(msg))
+ --print("Digiline: "..tostring(pos.x)..","..tostring(pos.y)..","..tostring(pos.z).."; Channel: "..tostring(channel).."; Message: "..tostring(msg))
  local meta = minetest.get_meta(pos)
  local mem = string.split(meta:get_string("mem"),"\n")
  local ms = ""