Hi,

Im trying to interface two 128Mbit SDRAMs (MT48LC8M16A2) to the
AT91RM9200, but it doesnt seem to be going right. I have a custom board for the AT91, and a seperate board for the SDRAM, the two are connected through an ordinary ribbon cable.

The master clock of the uC is running at 60Mhz. To test the integrity of the RAM, im writing data to a series of locations, say from 0x2000_0000 to 0x2000_0100. But when i read the data back, i find it to be garbled at *many* locations. I mean, instead of 0x11111111 that im writing, i get a 0xEff1111 or something at some locations, while on others the data is perfect. (im sending data out from the debug unit to HyperTerminal for debugging)

I have tried all permutations and combinations of the initialization sequence, but to no avail. Even tried changing both the ribbon cables (ive got one for the address lines, another for the data). What could be going wrong?? I dont think any of the SDRAMs has gone bad, because they both seem to have the correct data sometimes.

Could it be because of the fact that im using a seperate PCB for the SDRAM chips??

Thanx in anticipation
Mayank

this may be a silly recommendation so my apologies if it is inappropriate, but I had recently constructed a custom board which also shares the same external memory hierarchy as the DK (so we should have the same SDRAM chips). After debugging my board to full functionality, I would recommend that you test to be sure that every pin is soldered down well on both the SDRAM chips as well as the AT91. Although it is a long shot, it sounds as though "possibly" you have some address pin not making good contact, thus some addresses (which do not set the unconnected pin high) will write correctly, while others result in odd/unexpected placement of data even though the chip is otherwise working OK. I would not expect that the use of separate PCBs to introduce a problem, as long as the ribbon cable is not too long to produce timing issues with the 60MHz SDCK and you have a common ground between the boards.

In my experience, there is always one or two pins that "looked" like they made a good connection, yet when performing a continuity test with my trusty multimeter I would discover the connect was not made. This entire message is of course assuming you hand-soldered your custom board, and that you have not yet actually tested pin-by-pin the connectivity. It may be a pain, but it is worth it if it gets your design working Hope this helps,

Conger