No. PID was was not implemented in code - it was a stand alone PID controller and the temperature control fucntion itself was taken out of the code.
OK, so nopw you know. Temperature control of any stability (note: simple means will give good average) can only be achieved by PID control of the heating element. The heating element does not give a hoot whether the PID is in the code in your '51 or in an external chip.

Erik