Is this a high precision requirement ? if not you can consider using other SPI or I2C based digital thermal monitoring solutions and interface them directly to SPI or I2C ports of DSPIC.
In this case, you will need to connect the LM324 (again.. why quad Op-amp, and why not a 741 device ? ) to one of the ADC bits of DSPIC, configure that pin as "Analog type" in Microchip emulator setting and then access the ADC register internally and perform the temperature measurement in DSPIC...
Hope to be helpful