;enable RX interrupt 
;when char arrived led onboard is on
.equ	RXCIE0	= 7	
.equ	RXEN0	= 4	
.equ	UCSR0B	= 0xc1
.equ	UCSR0C	= 0xc2
.equ	TXEN0	= 3
.equ	UDR0	= 0xc6
.equ	bps	= 16000000/(16*9600) - 1
.equ	UBRR0L	= 0xc4	
.equ	UBRR0H	= 0xc5
.equ	UCSZ00	= 1
.equ	UCSZ01	= 2
.equ	URXCaddr	= 0x0024
.org 0x0
	jmp RESET		; Reset Handler
.org URXCaddr    ;USART, RX Complete Handler
	jmp _URXCaddr 
.org 0x60
RESET:	
	ldi	r16,LOW(bps)			
	ldi	r17,HIGH(bps)
	
	sts	UBRR0L,r16			
	sts	UBRR0H,r17
       ldi r16 ,(1 << UCSZ00) | (1 << UCSZ01)
       sts UCSR0C,r16
      ; Use 8-bit character sizes //[00]- no parity
      ;[0]- 1 stop bit, [011]- 8-bit data
      
      ;USART Receive Complete interrupt will be generated
      ;if RXCIE0 bit is written to one
      ;the Global Interrupt Flag in SREG is written to one
      ;and the RXC0 bit in UCSR0A is set
	ldi	r16,(1 << RXCIE0) | (1 << RXEN0)| (1 << TXEN0)
	sts	UCSR0B,r16
	sei
loop:	
	rjmp loop
_URXCaddr:
        cbi 5,5
        lds	r16,UDR0	
        cpi	r16,65			; compare r16 to "A"
	    breq	next
        ;sts UDR0,r16
        ;ldi r16,65
        ;sts UDR0,r16
        sbi 5,5
next:        
        reti

.equ	URXCaddr	= 0x0024	; USART Rx Complete
.equ	RAMEND	= 0x08ff
.equ	RXEN0	= 4	; Receiver Enable
.equ	RXCIE0	= 7	; RX Complete Interrupt Enable
.equ	SPL	= 0x3d
.equ	SPH	= 0x3e
.equ	RXCIE0	= 7	; RX Complete Interrupt Enable
; Definitions marked "MEMORY MAPPED"are extended I/O ports
; and cannot be used with IN/OUT instructions
.equ	UCSR0B	= 0xc1	; MEMORY MAPPED
.equ	UCSR0C	= 0xc2	; MEMORY MAPPED
.equ	UBRR0L	= 0xc4	; MEMORY MAPPED
.equ	UDR0	= 0xc6	; MEMORY MAPPED
.equ	UCSZ00	= 1	    ; Character Size
.equ	UCSZ01	= 2	    ; Character Size
.equ	DDRB	= 0x04
.equ	PORTB	= 0x05
 
.CSEG 
	RJMP MAIN 
.ORG URXCaddr 
	RJMP URXC_INT_HANDLER 
.ORG 40 
	MAIN: 
		LDI R16, HIGH (RAMEND) 
		OUT SPH, R16 
		LDI R16, LOW (RAMEND) 
		OUT SPL, R16 
		LDI R16, (1<<RXEN0)|(1<<RXCIE0)
		STS UCSR0B, R16 
		LDI R16, (1<<UCSZ00) | (1<<UCSZ01)  
		STS UCSR0C, R16 
		LDI R16, 0x67    ;9600 bauds 
		STS UBRR0L, R16
		LDI R16, 0xFF 
		OUT DDRB, R16 
		SEI 
	WAIT_HERE: 
		RJMP WAIT_HERE 
	URXC_INT_HANDLER: 
		LDS R17, UDR0 
		OUT PORTB, R17 
		RETI

-Arduino nano cnc shield v4.0 turn motor in avr asm

.equ DDRB=4
  .equ PORTB=5
  .equ DDRD=10
  .equ PORTD=11
  .equ PB0=0 ;ENABLE
  .equ PD2=2 ;STEP
  .equ PD5=5 ;DIRECTION

.org 0x60
init:
        ; arduino nano cnc shield v4.0
        sbi DDRB,PB0          ;pin ENABLE as output D8  PORTB,PB0
        sbi DDRD,PD5          ;pin STEP as output  D5    PORTD,PD5
        sbi DDRD,PD2           ;pin DIR as output  D2    PORTD,PD2
        cbi	PORTB,PB0          ; put pin ENABLE low D8 
loop:
        cbi PORTD,PD2          ;set DIR pin low
        call turn            ;turn motor 255 steps
        call wait3s         ;wait 1 second
        sbi PORTD,PD2           ;set DIR pin high
        call turn             ;turn motor 255 steps
        call wait3s         ;wait 1 second
	rjmp	loop           ;loop
pulse:
        ldi r17,30   ;motor velocity 5
        pause:
	dec	R16
	brne    pause
	dec	R17
	brne    pause
	ret
step:
	sbi	PORTD,PD5       ; put high pin STEP 
	rcall pulse        ;pulse
	cbi	PORTD,PD5        ;put low pin Step 
	rcall pulse         ;pulse
        ret
turn:
        call step
	dec	R20
	brne    turn
        ret    
 wait3s:
        ldi r18,100   ; wait 10
        waitx:
	dec	R16
	brne    waitx
	dec	R17
	brne    waitx
	dec	R18
	brne    waitx
	ret

shieldv4 con memory

.def	ZH	= r31
          .def	ZL	= r30
          .org 0x60
init:
        ; arduino nano cnc shield v4.0
        sbi 0x4,0          ;pin ENABLE as output D8  PORTB,PB0
        sbi 0xa,5          ;pin STEP as output  D5    PORTD,PD5
        sbi 0xa,2           ;pin DIR as output  D2    PORTD,PD2
        cbi	5,0          ; put pin ENABLE low D8 
	ldi	ZL, LOW (dithord*2)
	ldi	ZH, HIGH(dithord*2)
loop:
        inc r26
        cpi r26,10 ;how many from dithord
        brlo equal1 ;if 10
        rcall iar     ; again to 0
        equal1:    
        sbi 0xb,2    ; pin Direction high
	lpm	r25, Z+ ; load value from dithord and increment adress
        cpi r25, 1       ;if 1 
        breq equal
        cbi 0xb,2          ;set DIR pin low
        equal:      
        call turn            ;turn motor 255 steps
	rjmp	loop           ;again to loop
pulse:
        ldi r17,100   ;motor velocity 5
        pause:
	dec	R16
	brne    pause
	dec	R17
	brne    pause
	ret
step:
	sbi	0xb,5       ; put high pin STEP 
	rcall pulse        ;pulse
	cbi	0xb,5        ;put low pin Step 
	rcall pulse         ;pulse
        ret
turn:
        call step
	dec	R20
	brne    turn
        ret    
iar:
       	ldi	ZL, LOW (dithord*2)
	ldi	ZH, HIGH(dithord*2)
        ldi r26,0
        ret
dithord: .db 1,0,1,1,0,0,1,0,0,1,0,1,1,0,0,0,0,1,1,1,0,0

cnc shield v3.0

.equ DDRB=4
  .equ PORTB=5
  .equ DDRD=10
  .equ PORTD=11
  .equ PB0=0 ;ENABLE
  .equ PD5=5 ;STEP
  .equ PD2=2 ;DIRECTION

.org 0x60
init:
        ; arduino nano cnc shield v3.0
        sbi DDRB,PB0          ;pin ENABLE as output D8  PORTB,PB0
        sbi DDRD,PD2          ;pin STEP as output  D5    PORTD,PD5
        sbi DDRD,PD5           ;pin DIR as output  D2    PORTD,PD2
        cbi	PORTB,PB0          ; put pin ENABLE low D8 
loop:
        cbi PORTD,PD5          ;set DIR pin low
        call turn            ;turn motor 255 steps
        call wait3s         ;wait 1 second
        sbi PORTD,PD5           ;set DIR pin high
        call turn             ;turn motor 255 steps
        call wait3s         ;wait 1 second
	rjmp	loop           ;loop
pulse:
        ldi r16,250   ;motor velocity 5
        pause:
	dec	R16
	brne    pause
	ret
step:
	sbi	PORTD,PD2       ; put high pin STEP 
	rcall pulse        ;pulse
	cbi	PORTD,PD2        ;put low pin Step 
	rcall pulse         ;pulse
        ret
turn:
        call step
	dec	R20
	brne    turn
	dec	R21
	brne    turn
        ret    
 wait3s:
        ldi r18,100  
        waitx:
	dec	R16
	brne    waitx
	dec	R17
	brne    waitx
	dec	R18
	brne    waitx
	ret