A problem on Serial Window Display Mode

Hi,all
I have encountered a problem in debugging my appllication code with ISD51. This problem is that I could not select a HEX MODE for serial window#1.
As the ISD51 technical document said, I added the ISD51.A51 and ISD51.h in my project. Further more, I also added the startup.a51 module into the same project. In my main C function, I configured the Timer 2 as the baudrate generator of Serial Port UART and the the source code showed below. After all , I select the simulation debug utility of uVision2 to see if the ISD51 was initialized successfully. As the ISD51 Troubleshooting part showed me, I did all the steps like following.
1.Select Project - Options for Target - Debug: Use Simulator.
2.Start program simulation with Debug - Start/Stop Debug Session. This loads the user program in simulation mode.
3.Start running the user program (Debug - Go).
4.Entered the correct XTAL frequency in Project - Options for Target - Target - XTAL.(My selection is 11.0592MHz).
when I start Go command, the simulated serial port showed me a desired Baudrate 9600.
5.After then I openned the serial communication window (View - Serial Window#1), right-clicked in the Serial Window and want to select Hex Mode from the context menu. But in step, I failed. The ASCII mode could not be disabled. I also entered sin=0xA5 in the Command Window to Input a 0xA5 character in the serial input stream. The result in serial window#1 displayed a error code which I could not recognize, instead of the 0xF7 followed by six more hex values.
I do not know what is the problem and how to solve it. I wondered if you could give me hand? Thanks a lot.

/*************************************************************************************/
/* This application source code is used for study the ISD51 utility of Keil uVision2 */
/*                    System features are listed below                               */
/* Evaluatiom Board--------ZLG MCU/CPLD(Altera) Evaluatuion Board                    */
/* MCU -------- Philips P89C61x2BA    Crystal ------------ 11.0592MHz                */
/*************************************************************************************/

#include <reg52.h>
#include <intrins.h>
#include "isd51.h"

#define timer_2

void delay(void){
    long i;
    i = 0x800;
    while(i--);
}

void main (void)
{
    #ifdef timer_1                  /* use timer1 as baud rate generator            */
        SCON = 0x50;		        /* SCON: mode 2, 8-bit UART, enable reicever    */
        TMOD |= 0x20;               /* TMOD: timer 1, mode 2, 8-bit reload          */
        TH1 = 253;                  /* TH1:  reload value for 9600 baud @11.0592MHz */
        TR1 = 1;                    /* TR1:  timer 1 run                            */
        TI = 1;                     /* TI:   set TI to send first char of UART      */
        EA = 1;                     /* EA:   global interrupt enbale                */
    #endif
    #ifdef timer_2                  /* use timer2 as baud rate generator            */
        T2CON = 0x34;
        RCAP2H = 0xFF;
        RCAP2L = 0xDC;              /* 9600 baud @ 11.0592MHz                       */
        SCON = 0x50;                /* enable serial uart & receiver                */
        EA = 1;                     /* Enable global interrupt flag                 */
    #endif
	ISDinit();
    while (1){
        _nop_();
        _nop_();
        _nop_();
        _nop_();
        _nop_();
        _nop_();
        _nop_();
        _nop_();
        P1 = 0x00;
        _nop_();
        _nop_();
        _nop_();
        delay();
        P1 = 0xff;
        delay();
        _nop_();
        _nop_();
        _nop_();
    }
}