Hello Jeroen,
You should initialize R6 AND R7 in INIT subroutine. When
the 8051 is powered up R6 & R7 will probably set to FF.
This will mess up your of your table.
Regards,
Charles Bannister

Init:	
        mov	R6,	#00H	; reset caracter index
	mov	R7,	#00H	; reset bit index
	mov	TMOD,	#021h 	; Timer 1 in Auto-reload mode, timer 0 in 16 bit mode
	mov 	IE,	#000h 	; reset interrupts
	setb	ES		; enable serial interrupt
	mov 	PCON,	#080h	; set SMOD for 19200 baud  @11.0592 MHz
	mov	SCON,	#050h	; serial mode 1, REN=1
	mov	TH1,	#253	; load T1 for 19200 baud
	mov	TH0,	#0B4h	; set T0 for 0.05 sec @11.0592 MHz
	mov	TL0,	#095h	;
	setb	TR1		; start timer
	ret			; return