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External RAM access via 16-bit multiplexed bus

Aw S

Hello! I have problem with external memory access on XC167CI. The external RAM is organized on PLD. Need about 1 KB (64 kb non segment memory). I use 2-byte variables (unsigned int) to store on external RAM and 16-bit multiplexed bus. The address of one variable is 0x0400 - this is 16-bit address. In start_v2.a66 i check CS1 for start address is 0x000000. I use unsigned int near pointers. What settings i must do in CS1? And what types of variables and pointers to use for it?

Parents
  • 0 in reply to Aw S

    That depends on the memory model you use.
    If I use an external RAM e.g. start from 0x10000 and use small model, than I can access the RAM as an array variable.

    unsigned int xhuge arrRAM[0x20000];
...
for(i=0;i<0x20000;i++)
{
  if(read_RAM(i)=='0')
     {
     continue;
     }
  else
     {
     printf("\r\nError at %05d",i);
     break;
     }
}
    .

    A memory window has to start at a certain
    address described in the manual.
    The EBC you have to tell, which CS it has to use to access the address range.
    Than the EBC will compare the memory addresses against these settings and activate the CS.
    All ranges not specially given are handled per default by CS0.
    Adressing more than 64kB you need to configure extra address lines (segment address lines SALSEL), which are derived at XC167 from port P0H.

    I strongly recommend you to use DAvE for
    the setup, if you get some difficulties.

    Stefan

Reply
  • 0 in reply to Aw S

    That depends on the memory model you use.
    If I use an external RAM e.g. start from 0x10000 and use small model, than I can access the RAM as an array variable.

    unsigned int xhuge arrRAM[0x20000];
...
for(i=0;i<0x20000;i++)
{
  if(read_RAM(i)=='0')
     {
     continue;
     }
  else
     {
     printf("\r\nError at %05d",i);
     break;
     }
}
    .

    A memory window has to start at a certain
    address described in the manual.
    The EBC you have to tell, which CS it has to use to access the address range.
    Than the EBC will compare the memory addresses against these settings and activate the CS.
    All ranges not specially given are handled per default by CS0.
    Adressing more than 64kB you need to configure extra address lines (segment address lines SALSEL), which are derived at XC167 from port P0H.

    I strongly recommend you to use DAvE for
    the setup, if you get some difficulties.

    Stefan

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