I am currently working on test firmware for a system I have developed. The complexity and density of the design required the use of long signal traces for an included SD card slot. A combination of this and use of a flat cable to connect to an interface board has lead to a significant amount of ringing on the SD card lines. This inevitably caused various exceptions to be thrown using code that functioned correctly on a similar design. By adding a small capacitor (~20pF) on the clock line to ground, I have been able to clean up the clock signal edges enough that the SD card interface is functional. However, the cable used is now the critical issue. While a short, “perfect-world” cable allows for correct operation, some longer cables do not. Since the customer, for whom I am developing this system, will be sourcing/supplying the cables and developing some of their own firmware, I am hoping to develop a contingency plan, through firmware as well. Is it possible to decrease the SD card signal frequencies? If so, how can this be implemented? Thanks in advance for your time and consideration.