Here you go, If I remeber correctly this was set up for ~5 - 1200 Ohms for up to 33V feed,
It was intended to be a Constant Current / Constant Resistance Circuit, but your fine to keep it in constant resistance by selecting external Vref, switching to internal makes it constant current.
The 1M resistor is just for graceful shutdown, in the original purpose I wanted to switch off the DAC's when not needed, and the latch resistor was as a footprint for manually programming there ID's during setup,