sebitnt
Joined: 05 Dec 2010
Posts: 5
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| Multiple DS18B20 with parasite power |
 Posted: Wed Mar 02, 2011 11:52 am |
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Discussion thread here: http://www.ccsinfo.com/forum/viewtopic.php?t=44186
main.c
| Code: |
#include <16F877A.H>
#fuses XT,NOWDT,NOLVP,PUT,NOPROTECT,NOBROWNOUT,NOWRT
//#use delay(clock = 20000000)
#use delay(clock = 4000000)
#use rs232(baud=9600, xmit=PIN_C6, rcv=PIN_C7)
#define DQ PIN_E2 // One Wire Bus pin assignment
#include "onewire.c"
void main(void)
{
int8 i;
float temperature;
int8 scratch[9];
int8 numRom;
output_float(DQ); // Set as input. 4k7 pullup on bus.
FindDevices();
while(true)
{
if (!ow_reset()) // If a device is present
{
write_byte(0xCC,0); // Skip Rom command
write_byte(0x44,1); // Temperature convert command
//output_float(DQ);
delay_ms(750); // Max. conv. time is 750mS for 12 bit
//output_float(DQ);
ow_reset();
// Now get the device raw temperature data using Match ROM with the
// addresses obtained with FindDevices().
// If the received crc is same as calculated then data is valid.
// Scale and round to nearest degree C.
// Scaling is 0.0625 (1/16) deg.C/bit with default 12 bit resolution.
// Round by adding half denominator for positive temperatures and
// subtracting half denominator for negative temperatures.
for (numRom=1;numRom<=numROMs;numRom++)
{
if (Send_MatchRom(numRom))
{
write_byte(0xBE,0); // Read scratch pad command
dowcrc = 0;
// Get the data bytes
for (i=0;i<=7;i++)
{
scratch[i] = read_byte();
ow_crc(scratch[i]);
}
scratch[8] = read_byte(); // Get crc byte
ow_reset();
// If calculated crc from incoming bytes equal to crc byte
// then data is valid.
if (scratch[8] == dowcrc)
{
temperature = (float) make16(scratch[1],scratch[0]);
if (temperature >= 0)
temperature = (temperature + 8)/16;
else
temperature = (temperature - 8)/16;
printf("Sensor Number: %u", numRom);
printf(" %7.4g\r\n", temperature);
}
else
printf("Error in data\r\n");
}
}
printf("\r\n");
}
}
}
|
onewire.c
| Code: | // One Wire bus functions - from Dallas publication AN162
// "Interfacing DS18x20/DS1822 1-wire Temperature Sensor in a Microcontroller
// Environment". Delays calculated from values given for 8051.
// Changed variable name ROM[] to RomBytes[] because ROM is a reserved word
// in version 4 of the CCS compiler.
// Global variables
int8 RomBytes[8];
int8 lastDiscrep = 0;
short doneFlag = 0;
int8 FoundROM[12][8]; // Table of found ROM codes, 8 bytes for each
int8 numROMs;
int8 dowcrc; // crc is accumulated in this variable
// crc lookup table
int8 const dscrc_table[] = {
0,94,188,226,97,63,221,131,194,156,126,32,163,253,31,65,
157,195,33,127,252,162,64,30,95,1,227,189,62,96,130,220,
35,125,159,193,66,28,254,160,225,191,93,3,128,222,60,98,
190,224,2,92,223,129,99,61,124,34,192,158,29,67,161,255,
70,24,250,164,39,121,155,197,132,218,56,102,229,187,89,7,
219,133,103,57,186,228,6,88,25,71,165,251,120,38,196,154,
101,59,217,135,4,90,184,230,167,249,27,69,198,152,122,36,
248,166,68,26,153,199,37,123,58,100,134,216,91,5,231,185,
140,210,48,110,237,179,81,15,78,16,242,172,47,113,147,205,
17,79,173,243,112,46,204,146,211,141,111,49,178,236,14,80,
175,241,19,77,206,144,114,44,109,51,209,143,12,82,176,238,
50,108,142,208,83,13,239,177,240,174,76,18,145,207,45,115,
202,148,118,40,171,245,23,73,8,86,180,234,105,55,213,139,
87,9,235,181,54,104,138,212,149,203,41,119,244,170,72,22,
233,183,85,11,136,214,52,106,43,117,151,201,74,20,246,168,
116,42,200,150,21,75,169,247,182,232,10,84,215,137,107,53
};
// Returns 0 for one wire device presence, 1 for none
int8 ow_reset(void)
{
int8 presence;
output_low(DQ);
delay_us(488); // Min. 480uS
output_float(DQ);
delay_us(72); // Takes 15 to 60uS for devices to respond
presence = input(DQ);
delay_us(424); // Wait for end of timeslot
return(presence);
}
//******************************************************************************
// Read bit on one wire bus
int8 read_bit(void)
{
output_low(DQ);
delay_us(1); // Added, 1uS min. Code relied on 8051 being slow.
output_float(DQ);
delay_us(12); // Read within 15uS from start of time slot
return(input(DQ));
}
//******************************************************************************
void write_bit(int8 bitval)
{
output_low(DQ);
if(bitval == 1) {
delay_us(1); // 1uS min. Code relied on 8051 being slow.
output_float(DQ);
}
delay_us(105); // Wait for end of timeslot
output_float(DQ);
}
//******************************************************************************
int8 read_byte(void)
{
int8 i;
int8 val = 0;
for(i=0;i<8;i++)
{
if(read_bit()) val |= (0x01 << i);
delay_us(120); // To finish time slot
}
return val;
}
//-------------------------------------
//new byte writing routine with parasite power option
void write_byte(int8 val, int8 power_on)
{
int i;
for(i=0; i<8; i++)
{
output_low(DQ);
delay_us( 2 );
output_bit(DQ, shift_right(&val,1,0));
delay_us(60);
if((i == 7) && (power_on == 1))
{
output_high(DQ);
}
else
{
output_float(DQ);
delay_us( 2 );
}
}
}
//******************************************************************************
// One wire crc
int8 ow_crc(int8 x)
{
dowcrc = dscrc_table[dowcrc^x];
return dowcrc;
}
//******************************************************************************
// Searches for the next device on the one wire bus. If there are no more
// devices on the bus then false is returned.
int8 Next(void)
{
int8 m = 1; // ROM Bit index
int8 n = 0; // ROM Byte index
int8 k = 1; // Bit mask
int8 x = 0;
int8 discrepMarker = 0;
int8 g; // Output bit
int8 nxt; // Return value
short flag;
nxt = FALSE; // Reset next flag to false
dowcrc = 0; // Reset the dowcrc
flag = ow_reset();
if (flag||doneFlag) // If no parts return false
{
lastDiscrep = 0; // Reset the search
return FALSE;
}
write_byte(0xF0,0); // Send SearchROM command
do
{
x = 0;
if (read_bit() == 1) x = 2;
delay_us(120);
if (read_bit() == 1) x |= 1; // And it's complement
if (x == 3) // There are no devices on the one wire bus
break;
else
{
if (x > 0) // All devices coupled have 0 or 1
g = x >> 1; // Bit write value for search
// If this discrepancy is before the last discrepancy on a previous
// Next then pick the same as last time.
else
{
if (m < lastDiscrep)
g = ((RomBytes[n] & k) > 0);
// If equal to last pick 1
else
g = (m == lastDiscrep); // If not then pick 0
// If 0 was picked then record position with mask k
if (g == 0) discrepMarker = m;
}
// Isolate bit in ROM[n] with mask k
if (g == 1) RomBytes[n] |= k;
else RomBytes[n] &= ~k;
write_bit(g); // ROM search write
m++; // Increment bit counter m
k = k << 1; // and shift the bit mask k
// If the mask is 0 then go to new ROM
if (k == 0)
{ // Byte n and reset mask
ow_crc(RomBytes[n]); // Accumulate the crc
n++;
k++;
}
}
} while (n < 8); // Loop through until through all ROM bytes 0-7
if (m < (65||dowcrc)) // If search was unsuccessful then
lastDiscrep = 0; // reset the last Discrepancy to zero
else // Search was successful, so set lastDiscrep, lastOne, nxt
{
lastDiscrep = discrepMarker;
doneFlag = (lastDiscrep == 0);
nxt = TRUE; // Indicates search not yet complete, more parts remain
}
return nxt;
}
//******************************************************************************
// Resets current state of a ROM search and calls Next to find the first device
// on the one wire bus.
int8 First(void)
{
lastDiscrep = 0;
doneFlag = FALSE;
return Next(); // Call Next and return it's return value;
}
//******************************************************************************
void FindDevices(void)
{
int8 m;
if(!ow_reset())
{
if(First()) // Begins when at least one part found
{
numROMs = 0;
do
{
numROMs++;
for (m=0;m<8;m++)
{
FoundROM[numROMs][m] = RomBytes[m];
}
printf("Device No.%u address ",numROMs);
printf("%X%X%X%X%X%X%X%X\n\r",
FoundROM[numROMs][7],FoundROM[numROMs][6],FoundROM[numROMs][5],
FoundROM[numROMs][4],FoundROM[numROMs][3],FoundROM[numROMs][2],
FoundROM[numROMs][1],FoundROM[numROMs][0]);
} while (Next() && (numROMs<10)); // Continues until no additional
// devices found.
}
}
printf("\n");
}
//******************************************************************************
// Sends Match ROM command to bus then device address
int8 Send_MatchRom(int8 actNumRom)
{
int8 i;
if (ow_reset()) return FALSE; // 0 if device present
write_byte(0x55,0); // Match ROM
for (i=0;i<8;i++)
{
write_byte(FoundRom[actNumROM][i],0); // Send ROM code
}
return TRUE;
} |
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