Using LM70 temperature sensor with Arduino
There are several things that are not doing correctly. This is not a complete answer but to provide you some directions on how to get it right.

A0 is pin 54, it is not SS which is pin 53;

On how to use the SPI library properly, I would suggest that you read my blog on SPI, it will also help you to get the data out of data sheet that you need for SPI programming. Based on the timing diagram on the data sheet, you will need to configure the SPI as SPI_MODE2;

LM70 SI/O pin is used as both MOSI and MISO, you will need to connect MOSI to SI/O via a 10k resistor, and connect SI/O direct to MISO, this information is available in the data sheet;

LM70's temperature data is in Two's complement format, To convert it, it needs a little bit work. It is then need to shift down/right using bitshift operator by 5 bits to get ride of the first 5-bits, before finally multiply by 0.25C as per data sheet.


int value = 0x4b1f;  //value from SPI, temp = 125 degree C
int mask = 0x8000;   // mask for MSB
int temp = (-(value &amp; mask) + (value &amp; ~mask)) &gt;&gt; 5;
Serial.print(&quot;Temp&quot;);
Serial.println(temp*.25);

Read all links that I provided to understand the subjects and give it a try. Good luck!