"toggling" - 1 õppematerjal

Book Analog Interfacing to Embedded Microprocessors

Figure 2.14 SPI bus. The Maxim MAX1242 is a typical SPI ADC. The MAX1242 is a 10-bit suc- cessive approximation ADC with an internal S/H, in an 8-pin package. Figure 2.15 shows the MAX1242 interface timing. The falling edge of -CS starts a conversion, which takes a maximum of 7.5 ms. When -CS goes low, the MAX1242 drives its data output pin low. After the conversion is complete, the MAX1242 drives the data output pin high. The processor can then read the data a bit at a time by toggling the clock line and monitoring the MAX1242 data output pin. After the 10 bits are read, the MAX1242 provides two sub-bits, S1 and S0. If further clock transitions occur after the 13 clocks, the MAX1242 outputs zeros. Figure 2.15 shows how a MAX1242 would be connected to a microcon- troller with an on-chip SPI/Microwire interface. The SCLK signal goes to the SPI SCLK signal on the microcontroller, and the MAX1242 DOUT signal con- nects to the SPI data input pin on the microcontroller