In addition, a MAX232 type RS232 voltage level converter chip is In this project a SD card is connected to PORTC as follows: At the beginning of the main program, character array CID is declared to have 16 bytes. The program listing of the project is given in Figure 7.9 (program SD1.C). The 2.7V–3.6V supply required by the SD card is obtained via an MC33269DT-3.3 regulator with 3.3V output and is driven from the 5V input voltage.

The microcontroller is powered from a 5V supply which is obtained via a 7805-type 5V regulator with a 9V input. Serial output port pin RC6 (TX) of the microcontroller is connected to a MAX232-type RS232 voltage level converter chip and then to a 9-way D-type connector so it can be connected to the serial input port of a PC. This limits the maximum voltage at the inputs of the SD card to about 2.5V: Therefore, a potential divider is set up at the three inputs of the SD card using 2.2K and 3.3K resistors.

Maximum required input LOW voltage, VIL = 0.825VĪlthough the output produced by the card (2.475V) is sufficient to drive the input port of a PIC microcontroller, the logic HIGH output of the microcontroller (about 4.3V) is too high for the SD card inputs (maximum 3.6V).

Minimum required input HIGH voltage, VIH = 2.0625.

Maximum produced output LOW voltage, VOL = 0.4125V.

Minimum produced output HIGH voltage, VOH = 2.475V.

Figure 7.8: Circuit diagram of the projectĪccording to the SD card specifications, when the card is operating with a supply voltage of VDD = 3.3V, the input-output pin voltage levels are as follows:

Sd card cid