Posted on May 17, 2011 at 11:33The access mode used on the Eval board is not correct in regards with the RAM specification : the /DS (connected to /G) should not be low during the write access. Therefore, a modification to the ST9GP-EVAL PCB MUST be done by the user:
''2/ With some NVRAM lots, the memory cannot be accessed with the external memory access mode used on the Motherboard (MC=0, refer to the product datasheet). This mode is not compatible with all memory types as the DS signal is pulled down by the microcontroller during a WRITE Operation. In this case, the U1 component (74HC04) must be removed, and pins 3 and 4 must be connected together. Then the memory can be accessed using MC=1 mode (refer to the product datasheet). In this mode the OEN signal is pulled down only during the READ operation.''
Also, I have attached four different example codes for accessing the external RAM using mapped and unmapped data.
