Dear John.
As you already mentioned these inputs may be used for analogue or for digital signals.
How they are used is defined only by your program. If you for example select I07 it is a
digital input. If you select IA1 it is an analogue one. In fact you may use both within one
program if you think it makes sense (see attached example).
Therefore you may use voltages up to 24V and do not have to reduce it.
For analogue inputs everything above 10V is handled as value 1023.
For digital inputs at I07, I08, I11 and I12 everything below 8V is OFF and 8V and higher is ON.
For all other "pure" digital inputs the voltage level 0 to 5V is OFF and 15 to 28,8V is ON
Regards
Maikky