Ηandling MAX6675 Cold-Junction-Compensated K-Thermocouple to Digital Converter

[Dimitris Katsaounis]

The MAX6675 performs cold-junction compensation and digitizes the signal from a type-K thermocouple.
The data is output in a 12-bit resolution, SPI™-like, read-only format.
How it works:
Force CS pin low to output the first bit on the SO pin. A complete serial interface read requires 16 clock cycles. Read the 16 output bits on the falling edge of the clock. The first bit, D15, is a dummy sign bit and is always zero. Bits D14–D3 contain the converted temperature in the order of MSB to LSB. Bit D2 is normally low and goes high when the thermocouple input is open. D1 is low to provide a device ID for the MAX6675 and bit D0 is three-state.
My code:

sub MAX6675(Out Temp , Out D2bit)
Temp=0
'Force CS low to output the first bit on the SO pin
Set CS off
'Cycle the clock for dummy bit 15
Set SCK on
Set SCK off
'Read bits 14-3 from MAX6675
For i=1 to 12
Set SCK on
wait 1 ms
if SO=on Then
Temp=[word]Temp+1
else
Temp=[word]Temp+0
End if
Rotate Temp Left Simple
Set SCK off
Next i
'Read D2 Bit.
'Bit D2 is normally low and
'goes high when the thermocouple input is open
Set SCK on
wait 1 ms
if SO=on then
D2Bit=1
else
D2Bit=0
end if
Set SCK off
'Force CS High to stop transmition
Set CS on
Temp=[word]Temp/8
end sub

[Anobium]

Great posting.

Can we publish as an include file? See attached. Do you have time to update and test? And, could you document an example call to the method in the attached file? What are the requirements to make this work? Is it just SCK and CS? And, then, could you test be deleting your call to the original function and test using the new device.h file as an <include> file?

Great job.