This program is kind of simple. Might work. Add more loops if LED is blinking to fast.

mov r7,00001111

inc r3..............................A
cjne $50,r3,$FF...............NEXT
ajmp $30..........................goto A

mov r3,#00
inc r4
cjne $70,r4,$FF.................NEXT
ajmp $30.........................goto A

mov r4,#00
inc r5
swap r7............................swap 1111 and 000 in r7
.......................................output r7 to p1
cjne $90,r5,$FF.................NEXT
ajmp $30..........................goto A