Saving Old Instrument by Reverse Engineering It's Software

paul.delamusica wrote 05/26/2019 at 04:31 1 point

I have an old spectrophotometer, Thermo Spectronic 20 Genesys, circa 1996, according to the PCB marking. It consists of a stepping motor controlled by an Intel 80C251 microcontroller. It allows a user to input a wavelength and the controller would drive the motor to a predetermined angle. 

In order to arrive at the exact wavelength, the instrument keeps a set of local parameters for each machine. It is kept in an EEPROM on the main board, which unfortunately has been corrupted. Being old, the vendor no longer supports this model and no programming manual can be found. All I have is some circuit description and the circuit diagram. 

I would like to write to the EEPROM so that I can put new calibration data into it.  I don't know the data format nor the instructions for loading data through its RS232 port. On the plus side, I suppose that Intel 80C251 microcontroller is very common and the operation for driving a stepper motor is quite simple. Can this be done at all? Any advice is appreciated.