diff --git a/README.md b/README.md
index 2b5eb50..bb05770 100644
--- a/README.md
+++ b/README.md
@@ -1,6 +1,15 @@
-# test3d
+# Test3d
 Low-tech computing for Minetest
-## T400 instructions
+## Memory access
+Memory access in this mod occurs over digilines, with the channel as the prefix plus the memory address, and the message as either the new value or 'get' to get it returned, so for example:
+
+|Prefix	|Address	| Value	| Channel	| Message	|
+|-------|---------------|-------|---------------|---------------|
+|A	| 1		| 4	| A1		| 4		|
+|Default| 15		| get	| DefaultF	| get		|
+
+## T400
+### Instructions
 TOS = top of stack
 
 | ins	 | function			|    mnemonic	|
@@ -13,3 +22,6 @@ TOS = top of stack
 |4090	 | suptract TOS			| sub		|
 |4089	 | jump to TOS			| jmp		|
 |4088	 | skip if TOS = zero		| sez		|
+
+## T416
+The T416 is a 16-word memory. It stores 16 ints and is accessed as described in the Memory access section.