diff --git a/README.md b/README.md
index 9ff6754..2b5eb50 100644
--- a/README.md
+++ b/README.md
@@ -1,2 +1,15 @@
 # test3d
 Low-tech computing for Minetest
+## T400 instructions
+TOS = top of stack
+
+| ins	 | function			|    mnemonic	|
+|--------|------------------------------|---------------|
+|4095	 | duplicate TOS		| dup		|
+|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		|