ADS1248 control using SPI

Hello,

is it possible to contol the ADS1248 only by using the SPI pins nCS, SCLK, DIN and DOUT/nDRDY?

I don't use the CLK pin, because I select the internal oscillator. The nRESET pin is replaced by the SPI "RESET" command. If I use the combined function of the DOUT/nDRDY pin, the use of the nDRDY pin is not necessary. But what about the START pin? Do I have the same functionality by using the SPI "SYNC" command instead the START pin? 

I have a further question regarding the PGA: figure 53 in the datasheet shows the simplified diagram of the PGA. Are there some protecting diodes between the OPAMP inputs of A1or between the OPAMP inputs of A2?

thanks and best regards

Markus