1 files changed, 45 insertions, 0 deletions
diff --git a/src/org/blog/assembly/1.org b/src/org/blog/assembly/1.org
index 3fd21e4..7a712e3 100644
--- a/src/org/blog/assembly/1.org
+++ b/src/org/blog/assembly/1.org
@@ -241,3 +241,48 @@ d DB 5 DUP(1, 2)
 d DB 1, 2, 1, 2, 1, 2, 1, 2, 1, 2
 #+END_SRC
 Of course, you can use DW instead of DB if it's required to keep values larger then 255, or smaller then -128. DW cannot be used to declare strings.
+*** LEA
+LEA stands for (Load Effective Address) is an instruction used to get the offset of a specific variable. We will see later how its used, but first. here is something we will need :
+
+In order to tell the compiler about data type,
+these prefixes should be used:
+
+*BYTE PTR* - for byte.
+*WORD PTR* - for word (two bytes).
+
+For example:
+*BYTE PTR [BX]*     ; byte access.
+    or
+*WORD PTR [BX]*     ; word access.
+assembler supports shorter prefixes as well:
+
+b. - for BYTE PTR
+w. - for WORD PTR
+
+in certain cases the assembler can calculate the data type automatically.
+
+**** Example :
+#+BEGIN_SRC asm
+    org 100h
+    .data
+    VAR1 db 50h
+    VAR2 dw 1234h
+    .code
+    MOV AL, VAR1 ; We check the value of VAR1 by putting it in AL
+    MOV AX, VAR2 ; Same here
+    LEA BX, VAR1 ; BX receives the Address of VAR1
+    MOV b.[BX], 44h
+    MOV AL, VAR1 ; We effectively changed the content of the VAR1 variable
+    LEA BX, VAR2
+    MOV w.[BX], 5678h
+    MOV AX, VAR2
+#+END_SRC
+*** Constants :
+Constants in Assembly only exist until the code is assembled, meaning that if you disassemble your code later, you wont see your constant definitions.
+
+Defining constants is pretty straight forward :
+#+BEGIN_SRC asm
+    name EQU value
+#+END_SRC
+
+Of course constants cant be changed, and aren't stored in memory. So they are like little macros that live in your code.