The modular digital subsystem from ARC Technology provides real-time stimulus and response testing, enabling examination of devices heading into production. The system replaces the SR2500 and SR5000 series. It includes either VXI- or LAN-based interfaces and provides up to 512 I/O channels, with 1 Mbit per channel, 50 MHz clock rate, and real-time output data validation. The test state sequencer provides per-clock branch and looping control with a 32-level call stack. Additional conditional capability is available with a 16-level trace sequencer that provides logic analyzer-like triggering and trace capabilities. A software suite allows the rapid creation of complex digital stimulus and response patterns.