The EVM interfaces with the PHI and communicates with the computer over the USB. There are three devices on the EVM with which the PHI communicates: the two ADCs (over SPI) and the EEPROM (over I²C). The EEPROM comes preprogrammed with the information required to configure and initialize each ADC populated by default on the ADS704X-5XEVM. Therefore, communication with the EEPROM is only required if the user removes and replaces one of the default ADCs. See Section 2.4 for more information.

All ADCs supported by the ADS704X-5XEVM use SPI serial communication in mode 1 (CPOL = 0, CPHA = 1). The ADS704X-5XEVM offers 49.9-Ω resistors between the SPI signals to aid with signal integrity (see Figure 2-2) because the serial clock (SCLK) frequency can be as fast as 60 MHz. Typically, in high-speed SPI communication, fast signal edges can cause overshoot; these 49.9-Ω resistors slow down the signal edges to minimize signal overshoot. JP5 provides test points to measure the digital signals, as illustrated in Figure 2-7.

Figure 2-7 Digital Communication and PHI Connector on the ADS704X-5XEVM