Please refer to the PSoC 4 CapSense design guide for information on CSX sensing method. Let us know if you have any specific doubts in CSX, we would be happy to help.
In general, CSD measures the self capacitance between the sensor pad and ground. Whenever a finger is placed, Cf is added and this change in capacitance is measured by the CapSense IP to detect touch
On the other hand, CSX measures the mutual capacitance between two electrodes (Tx and Rx). Whenever a finger on a CSX sensor, the finger takes away some of the field lines going between the tx and rx electrodes. This reduces the field lines going between the tx and rx electrodes and therefore the mutual capacitance Cm reduces. This change in Cm is measured by the CapSense IP to detect touch.
CSX is almost independent of the Cp of the electrodes and is most suitable when the Cp of the sensors are too high due to long trace lengths.
CSX is ideal for touchpad as it supports multi touches unlike CSD which produces ghost effects.
The hardware tuning parameters are different for CSD and CSX. Please refer to the CapSense design guide for help on CSX tuning. The software tuning parameters are the same for both these methods.
We recommend you to use 4000S, 4100 S plus kits that has CSX based sensor patterns that is recommended by Cypress.
We also have many code examples to show how to tune CSX sensors and the firmware flow: