4850 OneWire Problem
Hi,
I am being defeated by a failure of OneWire Library to work with a PIC18F4580 using code which works with a PIC452,
Function Temperature:word;
var U:byte;
Temp:word;
begin
U:=0;
U:= Ow_Reset(PORTE,2);
// if U=0 then LED3:=1; Delay_ms(500); Led3:=0; // U=0 so presence pulse accepted
Ow_Write(PORTE,2,0xCC); // 0xCC seen on DQ
Ow_Write(PORTE,2,0x44); // 0x44 seen onDQ
Delay_us(120);
// The DQ line transmits a 500uS Low and the PRESENCE Rx is the response. Testing U confirms //that the master acknowledges the DS18S20 is present. It is powered by an external 5v, The 0xCC //and 0x44 commands are seen on the DD line
// OW-RESET REPEATED JUST TO TEST
U:=0;
U:= Ow_Reset(PORTE,2);
// if U=0 then LED3:=1; Delay_ms(500); Led3:=0; // U=0 so presence pulse accepted
Ow_Write(PORTE,2,0xCC); // 0xCC seen on DQ
Ow_Write(PORTE,2,0x44); // 0x44 seen onDQ
Delay_us(120);
Ow_Reset(PORTE,2);
Ow_Write(PORTE,2,0xCC);
Ow_Write(PORTE,2,0xBE);
// 0xCC and 0xBE seen on DQ master TX ,no response
Temp:=Ow_Read(PORTE,2);
Temp:=(Ow_Read(PORTE,2) shl
+ Temp;
// if Temp=0 then Delay_ms(500);LED3:=1; Delay_ms(500); Led3:=0;
//Temp=0 so no Temp Read = 0x00
Result:=Temp;
// Temp:=0 using PIC 18F4580
// Temp = ambient using PIC18F452
end;
Final bits 9 bit of both processors
PIC18F452
PIC18F4580
I find is difficult to make sense of these final transactions. It appears that my scope reads the final 9 bits as all Logic 1 high – suggesting the temperature processing has ended {?) but the 4580 does not return the LSB and MSB bytes. The only difference in the DQ line signal is the longer Low at the * shown for the 4580. That is the only difference seen in the complete transaction.
Can anyone suggest what might be wrong ? (I had to load the waveforms as files so the asterisk does not appear. Scrutiny of the two files may detect the longer low transition in the 4580 processor)
Many thanks,
Amfortas
