Flexbus SRAM deep problems

[GudeADS]

Hello,

we are using a MCF52259 board with Flexbus external 512KByte SRAM of type AS6C4008A 55ns. Our problem were bytes that occured on wrong places in the external SRAM when the MCU was on heavy duty. I wrote MarchC and MarchX RAM tests with 8, 16 and 32-bit access but I found no error. Finally we replaced the AS6C4008A 55ns with RAM of type IS62WV5128BLL 55ns and all our problems vanished. Until now we have no idea how to exact reproduce this errors, so that we could analyze them with a oscilloscope.

Has anybody experienced a similar behavior with Coldfire and SRAM on Flexbus? Any ideas how to reproduce this kind of error?

Best Regards,

Peter

[TomE]

I had similar problems with MCF5329 and SDRAM, detailed here:

https://community.freescale.com/message/66524#66524

Long story short. The MCF5319 defaults the bus pins to a high drive strength that was probably generating bad undershoots and overshoots on the bus. That caused memory corruption under high load. Reprogramming to a lower drive strength fixed the problem. Changing the BRAND of the chip also made the problem go away.

Unless you've got a long bus (which should then have bus terminators all over the place) you should be using the 2mA drive strength instead of the 10mA drive strength.

"Table 2-1. Pin Functions by Primary and Alternate Purpose" lists which bits in the PDSR, PDSRH and PDSRL registers control what pins.

You should also work through the detailed timing specifications of the port and the SRAM in case there's a problem with a setup or hold timing somewhere.

Tom