Ken has given a very good explanation for performing linear ramp up. You can even do non linear ramp up/down by putting the values inside the data memory DM[n], E.g.
DM[1] = 0
DM[2] = 10
DM[3] = 20
DM[3] = 40
DM[4] = 80
DM[5] = 160
You can use a variable as index (e.g. I) and at every internal you do the following:
IF I > 5 RETURN: ENDIF
SETDAC 1,DM
I = I + 1
Here you get an exponentially increasing DAC output!