http://www.cypress.com/?rID=2798 provides information on estimating output voltages (VOH, VOL) of the PSoC device's digital GPIO, when loaded at less than the rated maximum current. The internal routing resistances are presented for each of the listed PSoC 1 devices.
To learn about GPIO basics like how to configure drivemodes, interrupts and use shadow registers, please visit http://www.cypress.com/?rID=2900
