vault backup: 2022-07-28 11:14:22

content/notes/06-6809-programming.md

@@ -6,4 +6,61 @@ tags:
 - cosc204
 ---
 
+difficult
+- no variables
+- GOTO not loops
+- only compare ints and bytes
+- not really routines
+- all vars global
+- case sensitive
 
+# Hello World
+
+- need a routine that given a string will print each chracter one at a time
+- need to know how to print
+
+## Routines
+```
+routine:
+	rts
+```
+
+- no params
+- no local vars
+
+calling routine
+- lbsr, bsr, jsr
+- very subtle differences
+- we use bsr (branch to subroutine)
+
+```
+bsr routine
+```
+
+## Interation
+use GOTOs
+
+```
+	clra           //A = 0
+more:
+	cmpa #$06      //compare A to $06
+	beq done       //if equal, branch to done
+	inca           //increment a
+	bra more       //branch to more
+done:
+```
+
+- comparison only compares and sets flags in CC
+- you then branch on the result
+	- `beq bge` etc
+- other intructions set flags to
+	- `lda` etc
+- so
+
+```
+lda $45
+beq somewhere
+```
+
+## 6809.uk text screen
+![](https://i.imgur.com/dC1idMA.png)