Hi! It is very important what is the length of external memory address: is it one or two bytes? The next step you should learn something about space qualifiers. Look at examples for Raisonance RC-51:

#define BYTE unsigned char;

at 0x34 pdata BYTE device_1; <- 8-bits address
at 0x34 xdata BYTE device_2; <- 16-bits address

...
device_1 = 0x55; <- MOV A,#55H , MOVX @R0,A
device_2 = 0x55; <- MOV A,#55H , MOVX @DPTR,A
...

Sometimes (if you are using some devices conected to P1) it is very important to keep P1 stable using 8-bit adressing. Because if you are using xdata memory space, address is 16 bits long and P1 outputs MSB.

Jacek