1. Branching and Looping
Lecture L3.2

2. Branching and Looping 68HC12 Branch Instructions
Hex-to-ASCII Subroutine
Delay Loops

4. Branch Displacement

5. Negative Branch

8. How many times is the instruction INCB executed?

10. Bit-Condition Branch Instruction

13. Branching and Looping 68HC12 Branch Instructions
Hex-to-ASCII Subroutine
Delay Loops

14. Branching Example
1: ; Hex to ascii subroutine
2: ; input: A = hex value
3: ; output: A = ascii value of lower nibble of input
4: hexasc
5: F anda #$0f ;mask upper nibble
6: cmpa #$ ;if A > 9
7: bls ha1
8: B adda #$ ; add $37
9: D rts ;else
10: B ha adda #$ ; add $30
11: B 3D rts
Note: destination address = addr. of next instr. + displ.
0009 =

15. Branching and Looping 68HC12 Branch Instructions
Hex-to-ASCII Subroutine
Delay Loops

16. Note: addr. of next instr. + displ. = destination address 000A +FFF7
; ms_delay
; input: Y = no. of milliseconds to delay
ms_delay
pshx
0001 CE 07CF md1 ldx # ; N = ( )/4
md2 dex ; 1 ccycle
FD bne md2 ; 3 ccycle
dey
F bne md1 ; Y ms
000A pulx
000B 3D rts
Note: addr. of next instr. + displ. = destination address
000A
+FFF7
10001

17. Monitor routine to output ASCII character in A
; Delay test
outa equ $FF4F
ORG $800
#include hexasc.asm
#include ms_delay.asm
sec_delay
ldy #1000 ; 1000 ms delay
jsr ms_delay
rts
main
ldab #10 ; B = 10
mn1 tba ; A = B
jsr hexasc ; get ASCII value
jsr outa ; output to screen
bsr sec_delay ; delay 1 second
decb
bne mn1 ; do 10 times
swi
Monitor routine to output
ASCII character in A