Evaluating the in-system thermal performance should always occur by reading the system monitor circuitry (sometimes referred to as SYSMON or XADC) in the device. This integrated ADC can read an on-chip thermal diode, providing an accurate temperature reading. The diode is capable of delivering the junction temperature of the device during operation. Temperature specifications for a device are always relative to the SYSMON readings, not to case or other measurement points. For the device to be considered to operate within limits, the SYSMON temperature reading must account for any uncertainties in the temperature measurement, which can be found in the device datasheets. For example, an UltraScale+ device has an accuracy of ±3°C when using an external voltage reference. Therefore, for the device to be considered to operate within temperature specifications, the SYSMON reading should be at or below 97°C (100°C maximum operating temperature minus 3°C uncertainty). If the device supports temperature excursions, a SYSMON measurement should be at or below 107°C (110°C minus 3°C uncertainty). For Versal devices and subsequent generations, the uncertainty in device testing has been eliminated, simplifying the interpretation of measurements without any considerations for uncertainty. For Versal E and I-grade devices, a SYSMON reading of 100°C is considered within specifications (110°C when considering excursion). SYSMON data can be accessed either within the design circuitry or using the JTAG debug interface and the Vivado software.