Here you are a file for sending data to AT90S8515, although the chip is defferent, I think it could help. Here is the code in BOLD.
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.include "8515def.inc"
.def temp = r16
.org $000
rjmp start
.org $009
rjmp receiving
start:
cli
ldi temp,$5f
out spl,temp
ldi temp,$02
out sph,temp
ldi temp,$90
out ucr,temp
ldi temp,$40
out usr,temp
ldi temp,$33
out ubrr,temp
in temp,udr
ldi temp,$ff
out ddrc,temp
ldi temp,$ff
out portc,temp
sei
main_loop:
rjmp main_loop
receiving:
in temp,udr
com temp
out portc,temp
reti
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