I was trying to repair a circuit that contains the SUB-C501 microcontroller with external EPROM, SRAM and some gates. In order to repair it, i wrote a simple program in assembly and i send in Hyper Terminal a string. The program works fine in working circuis. But in circuits which have problem i do not take anything in Hyper Terminal and checking the circuit i measure something strange. I measure with oscillator the ports of high byte adress in Port2 and i see that all take some time level high, something that do not hapen in working circuits.
Does anyone cope with such a problem, does anyone can me explain what can be gong wrong?
The circuit that i send is not real because the rel one i do not have it because everything i take it in paper or in pc monitor. Is not that i do not want to show the circuit

...insert code here[/org 0
JMP START

START:
MOV A,#0xFF
MOV P1,A
MOV P3,A
MOV A,#0x7F
ANL PCON,A

MOV R0,0xFF
j0:	DJNZ R0,j0
MOV R0,0xFF
j1:	DJNZ R0,j1

AGAIN:
MOV TMOD,#0x20
MOV TH1,#0xFF
MOV SCON,#0x50
SETB TR1

SETB P1.4

MOV SBUF,#'A'
JNB TI,$
CLR TI


MOV A,#0xEF
ANL P1,A
CLR A

JMP AGAIN

;--------------------------------------
RECV:
	JNB RI,RECV
	MOV A,SBUF
	CLR RI
	RET
;--------------------------------------

END
]
thank you for every suggestion or advise