STP16CPC26 SDO output stuck low

[DSudo.2]

This is our first board design that uses the STP16CPC26. We have two chips daisy-chained together. The SDO output from the first chip never goes high. The SDO pin is definitely not shorted to ground or any other net, and is definitely connected to the SDI pin of the daisy-chained downstream chip. If the chip is properly powered, the SDI pin is held high, and clocks are applied to the CLK pin, is there any reason why the SDO pin would not go high?

[DSudo.2 · Accepted solution]

MHoll.2 solved the problem (thanks again!). The problem was that the MCU was powered by 3.3V and the LED driver by 5V. The MCU at 3.3V could not meet the input high voltage spec for the LED driver.