Ok, I gave up on trying to get the AD595 board working. I had a AD8495 board laying around I had forgotten about, but it turns out it appears it was bad as I could not get the proper readings from it, even just testing the ambient temperature without it being connected to the printer.
I broke down and bought a MAX31855 board. I have a configuration that I believe is working with that except it causes me to lose the ability to see my SKR card as a USB device on my print server so I can copy the firmware easily which with as many changes as I'm making to the firmware right now is a big deal.
FIrst I had the MAX board hooked to the SPI header on the board. I used pin 0.26 as the CS pin and the SCLK and MISO pins on the header. This didn't work until I set:
#define SDCARD_CONNECTION ONBOARD
Which then caused my ambient temperature to show up correctly, but I lost my USB functionality for my SD card and I could not use the LCD's SD card slot (reprap full graphic discount controller).
I then used the same pins, but defined the MISO and SCLK in configuration_adv.h which according to the comments should throw it into software SPI mode. I set the SDCARD_CONNECTION to LCD and I still was reading a temperature, and I could see the SD card on the LCD with all my GCode files, but still no USB support for the firmware SD Card.
Currently, I'm trying to use the SPI pins on the unused E1 driver slot, but that doesn't seem to work at all. Printer gives an immediate MINTEMP error and halts.
So, I'm confused about a few things. If I want to use Software SPI for the temperature probe, can I specify any open pins, or do they have to be ones designated for SCLK and MISO? I know I can specify any pins for the CS pin.
On this particular board, it looks to me like there are 2 hardware SPI ports surfaced at the SPI header and the EXP connectors where the LCD is attached. The ones in the printer driver pins aren't designated in the processor datasheet as actual SPI pins, but somehow get used as that on the board. Am I correct on those things?