Operation of the WB_TSPENDOWN is very simple and straightforward. Simply perform a Wishbone Read of the component and poll bit 0 of the 8-bit data word sent out on the component's DAT_O line. Bits 7..1 of this data are fixed as '0's.
When DAT_O(0) is '0', the TFT LCD panel's touch screen is being touched (for example a stylus is being held against it). When DAT_O(0) is '1', the touch screen is not currently being touched.
When the screen is found to be touched, enter the appropriate code routine accordingly for sending a control word to the Touch Screen Digitizer (AD7483), and hence initiate conversion.