Marcio,

So you decode (@C0XX-C7XXH) by assuring P2.7,P2.6=1; P2.5,P2.4=0; P2.3 is "Don't Care"? Are you using external ROM? If so have you qualified your I/O with PSEN?

You address C0XXH and write 55H twice with interrupts disable (critical region any intervening I/O causes trouble) and then perform config?

Because this device using indirect addressing (you write your address to Port 0, then your data to Port1) you are using a serial port to trace dumping IO address and IO data?

After config you write "AAH" to Port 0?

Perhaps your config look similar to:

  clr   ea         ;Disable Interrupts
  mov   dph,#0C0H  ; Address FDC
  mov   a,#55H     ;  Init Config Signal
  movx  @dptr,a    ;   Begin Config Operations
  movx  @dptr,a

;  *** DPTR is pointing to FDC Base REG (0C0H) ***
 
  clr   a          ;Init CR0 Register address
  movx  @dptr,a    ; Latch CR1 address
  inc   dph        ;  Port to Data Port 1
  mov   a,#3FH     ;   Init CR0 Initial Value
  movx  @dptr,a    ;    Update CR0

; *** Update next Configuration Register ***

  mov   dph,#0C0H  ;Re-address FDC Base Reg
  mov   a,#1       ; Init CR1 Reg address
  movx  @dptr,a    ;  Latch CR1 Register Addr.
  inc   DPH        ;   Address the Data Port 1
  mov   a,#9FH     ;    Update CR2
  movx  @dptr,a

;  *** continue thru all CRx Registers ***

  mov   dph,#0C0H  ;Re-address Port 0
  mov   a,#0AAH    ; Init the Config Terminator
  movx  @dptr,a    ;  Indicate Config Complete

  setb  ea         ;Enable Global Interrupts
  ret              ; Exit

As you no doubt recognize this is the data sheet init routine in 8051 mnemonics.

regards,
p