Question: how to measure voh and vol?
Answer: Step 1: Power the DUT by applying VDD ... 
Step 2: Condition the DUT outputs to the logic-high state. ... 
Step 3: Set the SMU to sink a small current (VOH), or source a small current (VOL) ... 
Step 4: Connect the DUT pin to be tested. ... 
Step 5: Measure the output voltage. ... 
Step 6: Switch to the next pin and repeat.