b9823103_ammer_for_ARM_and_Cortex_cores__Description
[Pin] 11 [Signal] RTCK [Type] Input [Description] 
Return test clock signal from the target. Some targets must synchronize the JTAG inputs to internal clocks. To assist in meeting this requirement, you can use a returned, and retimed, TCK to dynamically control the TCK rate. Flasher ARM supports adaptive clocking, which waits for TCK changes to be echoed correctly before making further changes. Connect to RTCK if available, otherwise to GND.
SEGGER | Flasher ARM | Flash Programmer for ARM and Cortex cores
Description