What is EXTEST mode? - What is EXTEST mode? Description EXTEST is mandatory IEEE Std. 1149.1 Joint Test Action Group (JTAG) instruction. It tests the "external" traces of a device. Resolution The following steps provide a brief explanation of how the EXTEST testing works: The boundary scan register is connected between TDI and TDO and the device is placed in an “external” test mode Boundary-scan output cells (the source) drive a known logic high and low value onto the trace being tested. Boundary-scan input cells (the destinations) connected to this trace capture the value on this trace. If the expected values match, the trace is fine. If not, the trace is either open or shorted. The high-impedance state of EXTEST is overridden by bus hold and weak pull-up resistor features. Related Articles Why doesn’t the capture phase of the EXTEST instruction capture the correct data values for the my MAX® 7000S device I/O pins during JTAG boundary-scan testing? Custom Fields values: ['novalue'] Troubleshooting NA False ['novalue'] ['novalue'] novalue novalue ['Programmable Logic Devices'] ['novalue'] ['novalue'] ['novalue']