There is no need to reset 8255. Reset only clears the control register and all ports are set to the input mode. You can do it by software or you can set any other mode if you wish.
To Peter:
Your program :

MOV PSW,#00H     ;no matter for this program
MOV DPH,#0F0H
MOV DPL,#11H     ;there is single mov dptr,#nn command!

MOVX @DPTR,A
MOV DPH,#0F0H
MOV DPL,#00H
MOV A,#55H
MOVX @DPTR,A

There is no

sjmp $

command here !!

You have to check :
A0,A1,RD,WR of 8051 system is connected to A0,A1,RD,WR of 8255 properly?
RESET of 8255 is LOW after poweron?