Clock Skew
Phase timing differences between test clock signals arriving at different integrated circuit boundary-scan pins induce synchronization errors across JTAG scan chains. Test engineers measure TCK clock skew during boundary-scan infrastructure validation and automated test program generation. This timing variation excludes operational system clock skew occurring on functional logic nets.
Scan Timing
Boundary-scan architecture relies on a common test clock line distributed across multiple compliant integrated circuits on a printed circuit board. When physical routing lengths, buffer propagation delays or capacitive loading differ along TCK branches, TCK clock skew shifts clock edge arrivals between neighboring devices. If a downstream device receives its clock edge before an upstream device, serial test data shifted out of the first device may corrupt data latching in the second device.
Signal integrity analysis on JTAG chains requires balanced tree routing or termination buffers to minimize timing skew across long chains. Automated test equipment detects scan chain shift errors caused by clock skew during initial boundary-scan setup routines. Adding delay buffers or matching clock trace lengths preserves valid setup and hold timing margins between scan registers.
Synchronization Limit
Timing imbalances across test clock lines cause scan chain failure and false fault reporting. Balanced routing trees maintain synchronous edge alignment across all boundary-scan devices. Test validation verifies clock edge synchronization before running automated structural tests.
