The Early Microcontroller : 80C39 is a CMOS Version of 8048 the one that preceded 8031-8051. MCS48 is the set for that, MCS51 is the current set.
Digital to Analog Converter with uC Watchdog is the front end and an external hardware watchdog of an early kind. These are simple but robust circuits and worked well in noisy environments.
Here is an example project for 80C39-8748-8749 microcontroller. This code was written by me, and it works. But the documentation is not complete or may have errors.
Process Controller code here 80C39 Code for MCS48 (editable spreadsheet online)
The circuit for these are on this page along with other circuits. This may be difficult to put together now. But
the code and hardware is near compatible to 8051 uC. Now there are may types of ADC and uC.
Voltage to Frequency Converter AD Interface is the analog front end of this instrument. Uses a LM331 VCO. The Signal conditioning too is integrated in this circuit.
This was supposed to have Analog in and Analog out. Some parts of the circuit may be in the 80C51 page. This has ramp-up and ramp-down settings for the Increment and Decrement buttons. This helps setting setpoint quickly. There is also debouncing for the pushbutton.