Incircuit

Incircuit is a term used to describe actions performed with a circuit still assembled on a printed circuit board. It usually appears as in-circuit or incircuit and is used to describe several electronics practices that operate without disassembling the assembly.

In-circuit testing (ICT) verifies electrical performance of a populated PCB. ICT uses fixtures or automated test equipment to apply signals and measure responses at multiple points, checking for shorts, open circuits, incorrect component values, and other faults. Some ICT methods employ boundary-scan (IEEE 1149.1) to access nets without direct probes.

In-circuit programming loads firmware into memory devices such as microcontrollers while the device remains on the board. Programming interfaces include SPI, I2C, or UART, and the process is common in manufacturing to deploy software or firmware without removing parts.

In-circuit debugging uses hardware interfaces to inspect the running circuit. Techniques include in-circuit emulators or debuggers that connect via JTAG or SWD, allowing breakpoints, memory inspection, and stepwise execution while the circuit is powered.

Limitations of incircuit approaches include reliance on accessible test points, potential interference with normal operation, and reduced coverage on densely packed or high-speed nets.