When an FPGA mezzanine card (FMC) is attached to J26, it is automatically added to the JTAG chain through electronically controlled single-pole single-throw (SPST) switch U45. The SPST switch is normally closed and transitions to an open state when an FMC is attached. Switch U45 adds an attached FMC to the JTAG chain as determined by the FMCP_HSPC_PRSNT_M2C_B signal. The attached FMC card must implement a TDI-to-TDO connection using a device or bypass jumper to ensure that the JTAG chain connects to the U1 XCZU28DR RFSoC.