I am developing a 8052-based (AT89c52) SBC with the following features / ICs.

-> 1 X 8K SRAM (@ 0000h ~ 1FFFh)
-> 1 X 32K SRAM (@ 2000h ~ 9FFEh)
-> 1 X 32K FLASH ROM (@ 0000h ~ 7FFFh)
-> DS12287 RTC
-> 8259A (PIC Interrupt controller)
-> 2 X 8255A (PPI)
-> 1 X 8279 (Keyboard & Display controller)
-> Auxilary Output port (74HC573)
-> Auxilary Input port (74HC245)
-> LCD (Memory mapped I/O)
-> Serial EEPROM (93c56 - connected to P1 lines)
-> Multiplexed Serial ports - controlled by P1.1 (0 = RS232 / 1 = RS485).

Now, the RAM, FLASH ROMs and 8259 and the Address decoders are on BOARD-1, and the rest of the stuff is on BOARD-2. Its a wire-wrap design so far. I wanted to test my code and the system functionality first and then go for final PCB developments.

The 2 boards are connected by jumper headers and data cables. Now, i can access almost every function on teh boards except RAMs. When i write-to OR read from RAMs, it returns absured data.

If i disconnect BOARD-2, it works fine. With BOARD-2 connected, the 8255s and 8279 work fine. Even the FLASH ROM is working fine, since the code is executing off of it. I am assuming that the data bus is unable to handle the load of so many ICs, so when i disconnect the data-bus from BOARD-2, it works fine.

Hence, i added a 74HC245 bus buffer/transciever on teh data-bus so as to divide the load, but it does not work even then. Can anyone help me out?

I can send a detailed schematic diagram and code to anyone willing to look into it.

Thank you.
Zeeshan.