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Ram storage of long intergers to be modified by Modbus

 
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cam_male2003



Joined: 21 Sep 2005
Posts: 12

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Ram storage of long intergers to be modified by Modbus
PostPosted: Tue Nov 01, 2005 8:12 am     Reply with quote

How is a long stored in ram? I just want to verify that this is right. If the Value is 50.
unsigned long maxdiff;
#byte maxdiff= 74

It stores it at location 74 is 50
and location 75 as 0

I want to modify the values in ram, is there an easy way to do this. Since modbus writes MSD to LSD, not LSD to MSD?

If I have a floating Number how do I handle that?

Lost in the fog... lol
Neutone



Joined: 08 Sep 2003
Posts: 839
Location: Houston

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PostPosted: Tue Nov 01, 2005 9:08 am     Reply with quote

This is an example from a post I made. It does have to swap the byte order as it copies the register locations into the packet.
Code:
               for(y=start;y<finish;y++)
               {  x=(y*2)+1;
                  COMM1_Buffer[Index] = REG_Map[x];
                  Index++;
                  --x;
                  COMM1_Buffer[Index] = REG_Map[x];
                  Index++;
               }
REG_Map is a byte array at the same location as a int16 array.
Code:
Int16 Registry_Map[128];
#locate Registry_Map = 0x200
Int8  REG_Map[256];
#locate REG_Map = Registry_Map
MikeValencia



Joined: 04 Aug 2004
Posts: 238
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PostPosted: Tue Nov 01, 2005 9:39 am     Reply with quote

I modified the sample code in the FAQ that stores a float in eeprom so that it stores and reads a long int (2 bytes) in eeprom. I suppose you can re-use the for-loops for your app.

Code:
unsigned long READ_LONG_INT_EEPROM(long int n)
{
    int i;
    long int data;
   
   for (i = 0; i < 2; i++)
        *(&data + i) = read_eeprom(i + n);
    return(data);
}

void WRITE_LONG_INT_EEPROM(long int n, long int data)
{
    int i;

    for (i = 0; i < 2; i++)
    {
        write_eeprom(i + n, *(&data + i) ) ;
    }
}
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