Problem while accessing external RAM.

Hi,

I am using AT89S52 MCU as a target device.
The idea here is to access (Read/Write) internal registers of an peripheral IC DS21554 from Dallas. I will be accessing this registers as external RAM memory locations.

Now, i checked whether the pins RD(P3.7) & WR(P3.6) are asserted (goes low) automatically using Logic Analyzer while executing the following code:

volatile unsigned char xdata ptr _at_ 0x4000;
void main(void)
{ unsigned char charVal; ptr = 0x55; // Write. charVal = ptr; // Read.
}

But, it didn't happen the way expected.

Since, in this code a we are trying to read and write to external data memory location, ideally RD(P3.7) and WR(P3.6) should go low. So, is there anything wrong with the code i am using and if it is then please suggest the right way to do so.