Looks like a 1/2R of Felipe V--from Mexico City--from the period 1701 through 1733.
If its weight is between 1.6 to 1.7 grams it's a 1/2R. If about 3.5 grams, then it's a1R.
The date would be in the 10 o'clock position (off the coin) and the assayer's initial is below the 'M' .
The choices for an assayer are I, J. D, R. and MF; yours appears as a 'D'.
Don in SoCal