[U-Boot] Not able access External peripherals in PPC440EP

Hi, I am using a PPC 440EP processor based custom designed board which is based on AMCC's Yosemite as reference design. I have ported u-boot-1.1.6 onto it. It is working fine but not able to access external peripherals like NVRAM, ADC, DAC etc. in the board. When try to read those addresses with MD command it is generating exception. Can anybody please help me how to access them

Regards Suresh