KA 21 is hardware solution for Gayle PCMCIA reset bug. The Gayle chip in Amiga 1200 does not reset PCMCIA card during system reset event (for example keyboard reset). Then some cards are not working after such event until the Amiga is powercycled. KA 21 generates forced CC_RESET high pulse from system reset signal. The device is installed directly on the Gayle chip.
KA21 cannot be used together with Elbox FastATA. The reason is FastATA has its own board mounted on Gayle chip.