diff --git a/main.S b/main.S
index e2f268c..89c8ea5 100644
--- a/main.S
+++ b/main.S
@@ -33,10 +33,10 @@
 
   .section ".rodata","a"
 screendata:
-  .byte   0b00000001
-  .byte   0b00000011
-  .byte   0b00000111
-  .byte   0b00001111
+  .byte   0x01
+  .byte   0x03
+  .byte   0x07
+  .byte   0x0f
 screendataend:
   .byte   0xff
 red:
@@ -79,9 +79,10 @@ _start:
 
 init:
   ;; configuration of GPIO Ports
-  mov.b   #BIT0|BIT1|BIT2, &P1DIR
-  mov.b   #BIT1|BIT4, &P2DIR
-  mov.b   #BIT1|BIT4, &P2SEL
+  mov.b   #BIT0|BIT1|BIT2,&P1DIR
+  mov.b   #0,&P1OUT
+  mov.b   #BIT1|BIT4,&P2DIR
+  mov.b   #BIT1|BIT4,&P2SEL
 
   ;; timer configuration
   ;;  configure and stop timer
@@ -98,17 +99,14 @@ init:
   mov.w   #OUTMOD_7, &TA1CCTL2
 
   ;; initialize bit-counter for isr
-  mov.b   #BIT_COUNTER_INIT_VALUE, BIT_COUNTER_REGISTER
-  ;; initialize isr-sync register
-  mov.b   #SIGNAL_INIT_VALUE, SIGNAL_REGISTER
+  mov.b   #0x01,r6
+  ;; initialize isr-sync register, signal BYTE_DONE for the first start
+  mov.b   #0x01,r4
 
-  ;; screen data start/next into DATA_NEXT_ADDRESS_REGISTER
-  mov.w   #screendata, DATA_NEXT_ADDRESS_REGISTER
-  ;; screen data end into DATA_LAST_ADDRESS_REGISTER
-  mov.w   #screendataend, DATA_LAST_ADDRESS_REGISTER
-  ;; load first screen data value into DATA_BYTE_REGISTER
-  mov.b   @DATA_NEXT_ADDRESS_REGISTER, DATA_BYTE_REGISTER
-  inc.w   DATA_NEXT_ADDRESS_REGISTER
+  ;; screen data start/next into r7
+  mov.w   #screendata, r7
+  ;; screen data end into r8
+  mov.w   #screendataend, r8
 
   ;; start timer in up mode
   bis.w   #MC0, &TA1CTL
@@ -118,16 +116,12 @@ init:
 
 mainloop:
   ;; prepare next byte to handle by isr
-  ;; first, check whether we are already at the end of screen data
-  cmp.w   DATA_NEXT_ADDRESS_REGISTER, DATA_LAST_ADDRESS_REGISTER
-  jnz     mainloop_prepare_next_byte
-  ;; in that case rollover to the start again
-  mov.w   #screendata, DATA_NEXT_ADDRESS_REGISTER
-mainloop_prepare_next_byte:
-  ;; load the byte from the screen data next pointer
-  mov.b   @DATA_NEXT_ADDRESS_REGISTER, NEXT_DATA_BYTE_REGISTER
-  ;; and increase the pointer
-  inc.w   DATA_NEXT_ADDRESS_REGISTER
+  cmp.w   r7,r8
+  jz      mainloop_data_done
+
+  ;; load next data byte
+  mov.b   @r7,r9
+  inc.w   r7
 
 mainloop_wait_for_isr:
   ;; check bit0 in sync register, wait for the signal from 
@@ -136,50 +130,64 @@ mainloop_wait_for_isr:
   jz      mainloop_wait_for_isr
 
   ;; load data
-  mov.b   NEXT_DATA_BYTE_REGISTER, DATA_BYTE_REGISTER
-  ;; clear the signal
-  bic     #SIGNAL_BYTE_DONE, SIGNAL_REGISTER
-  ;; mark the cycle
-  bis     #BIT2, &P1OUT
-  bic     #BIT2, &P1OUT
+  mov.b   r9,r5
+  ;; clear BYTE_DONE
+  bic     #0x01, r4
+  ;; enable isr
+  bis     #0x02, r4
 
   ;; continue
   jmp     mainloop
 
+mainloop_data_done:
+  ;; signal all data processed, isr finish
+  bis     #0x04, r4
+  bis     #BIT2, &P1OUT
+  ;; continue
+  jmp     mainloop
+
 
 ; --- timer isr ---
   ;; r6: exclusively used by isr as bit-counter
 timer1_a0_isr:
-  ;; func begin marker
-  bis     #BIT0, &P1OUT
-  ;; check isr idle bit
-  bit     #SIGNAL_ISR_ENABLE, SIGNAL_REGISTER
-  jnz     timer1_a0_isr_exit
+  ;; check isr enable bit
+  bit     #0x02,r4
+  jz      timer1_a0_isr_exit
 
-  ;; shift msb of data register r5 into carry flag and set or reset P1.1 accordingly
-  rla.b   DATA_BYTE_REGISTER
+  ;; shift msb of data register r5 into carry flag and set or reset P1.0 accordingly
+  rla.b   r5
   jnc     timer1_a0_isr_false_bit
-  bis     #BIT1, &P1OUT
+  bis     #BIT0,&P1OUT
   jmp     timer1_a0_isr_end
 timer1_a0_isr_false_bit:
-  bic     #BIT1, &P1OUT
+  bic     #BIT0,&P1OUT
    
-  ;; shift bit-counter, after eight shifts signal byte done and reset bit-counter
 timer1_a0_isr_end:
-  rla.b   BIT_COUNTER_REGISTER
+  ;; enable output
+  bis     #BIT1, &P1OUT
+
+  ;; roll bit-counter
+  rla.b   r6
   jnc     timer1_a0_isr_exit
 
   ;; reset bit-counter
   mov.b   #BIT_COUNTER_INIT_VALUE, BIT_COUNTER_REGISTER
   ;; signal byte done
-  bis     #SIGNAL_BYTE_DONE, SIGNAL_REGISTER
+  bis     #0x01,r4
+
+  bit     #0x04, r4
+  jz      timer1_a0_isr_exit
+  ;; disable isr
+  bic     #0x02, r4
+  ;; disable output
+  bic     #BIT1, &P1OUT
 
 timer1_a0_isr_exit:
-  ;; func end marker
-  bic     #BIT0, &P1OUT
   reti
 
 
+  .section "__interrupt_vector_14","ax",@progbits
+  .word   timer1_a0_isr
 
   ;; .resetvec comes from linker
   .section ".resetvec","ax",@progbits