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Futterama
Joined: 17 Oct 2005
Posts: 98
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| Storing 10bit ADC value in internal EEPROM |
 Posted: Tue Feb 07, 2006 5:21 am |
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Hello forum,
I would like to store the 10bit ADC value from the ADC on a PIC12F675 into the internal EEPROM. My problem is my limited C knowledge.
I would like to store 4 10bit readings in 5 EEPROM addresses.
So how do I split the 10bit readings into 8bit segments?
I was thinking:
1. Store 4 10bit readings in 16bit integers.
2. Take the first 10bit reading and put the 8 LSB in the first EEPROM address.
3. Take the 2 MSB in the first 10bit reading and add the 6 LSB of the second 10bit reading and store this in the second EEPROM address.
4. Take the 4 MSB of the second 10bit reading and add the 4 LSB of the third 10bit reading and store this in the third EEPROM address.
5. You get the idea, right?
But I'm having problems contructing a 8bit int from the 16bit int.
How do I "extract" certain bits from an integer, and how do I put them into another integer?
I hope you can help me. Thanks.
Regards,
Futterama |
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dan king
Joined: 22 Sep 2003
Posts: 119
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| Posted: Tue Feb 07, 2006 7:19 am |
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You can simply store the lsB by copying the 16b var into a 8 bit, the msB will be discarded. Then shift the 16 bit variable 8 places and store that result into the msB. An example follows where temp_val is 16bit and msb and lsb are 8 bit.
| Code: | lsb = temp_val;
msb = (temp_val >>8);
write_eeprom(1,lsb);
write_eeprom(2,msb); |
As far as packing the data into fewer locations, you'll have to play with manually masking( logical AND) and merging (logical OR).
Hope this helps. Let me know if you need more assistance.
Dan |
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Futterama
Joined: 17 Oct 2005
Posts: 98
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| Posted: Tue Feb 07, 2006 7:34 am |
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I found a way to do it after much testing.
I made this function that will return the number of LSBs given:
| Code: | int8 GetBits(int16 FromLongint, int8 BitsToGet)
{
int8 result = 0;
int8 temp, i;
for(i=0; i<BitsToGet; i++)
{
if(FromLongint & 0x01)
temp = 128;
else
temp = 0;
result = result | temp;
if(i<BitsToGet-1)
result >>= 1;
else
result >>= 8-BitsToGet;
FromLongint >>= 1;
}
return result;
} |
I'll just have to make a simular function that will return a number of MSBs. |
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Tttelmah
Guest
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| Posted: Tue Feb 07, 2006 7:45 am |
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| Code: |
int8 store[5];
void put10(int16 val,int8 locn_number) {
//Save a ten bit value to a single 8bit location, plus two
//bits in fifth byte.
int8 bits;
store[locn_number]=make8(val,0); //put the LSB into the array
store[4]&=(0HFC << locn_number); //clear bits to write
bits=(make8(val,1) & 3) << locn_number;
store4|=bits; //insert the extra two bits
}
int16 get10(int8 locn_number) {
//retrieve a 10bit value from the array
int8 mask;
mask=(store[4] >> locn_number) & 3; //retrieve the two bits
return make16(mask,store[locn_number]);
}
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Untested, but the basic idea should work.
You will need to read the whole array out of eeprom, before retrieving a value using 'get10'. This will accept location numbers from 0 to 3, to access the four values. Similarly, once updated with 'put10', you will need to save at least the bottom byte, and the fifth byte to the eeprom.
Best Wishes |
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Futterama
Joined: 17 Oct 2005
Posts: 98
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| Posted: Wed Feb 08, 2006 4:53 am |
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I'll just post my final code here:
| Code: | int8 FourMSBs = 0;
int8 LSBs_address = 0;
int8 MSBs_address = 4;
int8 HelpAddress = 0;
void WriteEEPROM(int8 address, int8 data)
{
// Write byte
EEIF = 0; // Clear interrupt flag
EEADR = address; // Set write address
EEDATA = data; // Set data to write
WREN = 1; // Enable EEPROM Write
EECON2 = 0x55; // Following write sequence
EECON2 = 0xAA; // Following write sequence
WR = 1; // Initiate write
while(!EEIF); // Wait for the write sequence to complete
WREN = 0; // Disable EEPROM Write
EEIF = 0; // Clear interrupt flag
}
int8 ReadEEPROM(int8 address)
{
// Read byte
EEADR = address; // Set read address
RD = 1; // Initiate read
return EEDATA; // Return data
}
void SaveToEEPROM(int16 data)
{
int LSB, MSB;
LSB = data; // Get the 8 LSBs
MSB = (data >> 8); // Get the 8 MSBs (there is only 2)
WriteEEPROM(LSBs_address, LSB); // Write LSBs to EEPROM
LSBs_address++; // Increment the LSB memory address
HelpAddress++; // Increment the help address
if(HelpAddress == 1)
FourMSBs = FourMSBs | MSB; // Put MSBs into bit 0 and 1
if(HelpAddress == 2)
FourMSBs = FourMSBs | (MSB * 4); // Put MSBs into bit 2 and 3
if(HelpAddress == 3)
FourMSBs = FourMSBs | (MSB * 16); // Put MSBs into bit 4 and 5
if(HelpAddress == 4)
FourMSBs = FourMSBs | (MSB * 64); // Put MSBs into bit 6 and 7
WriteEEPROM(MSBs_address, FourMSBs); // Write MSBs to EEPROM
if(LSBs_address == MSBs_address) // If the LSB address equals the MSB address (4, 9, 14, 19, 14, 29 ect.)
{
LSBs_address++; // Increment the LSB memory address
MSBs_address = MSBs_address + 5; // Increment the MSB memory address by 5
FourMSBs = 0; // Reset variable
HelpAddress = 0; // Reset variable
}
} |
In the EEPROM the data will be placed like this:
| 8LSBs | 8LSBs | 8LSBs | 8LSBs | 8MSBs from prev. 4 bytes | |
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