To know the slave address for this device, you have to read the Extendable Soft Addressing on page 9 in the datasheet.
Next you have to write to the Port Select Register (18h) with 0 (for GPIO Port0).
Then you have to write the Pin Direction Register (1ch) with the bit numbers which are connected to LEDs as 0 (output) and the rest as 1 (input)
Then you have to write to the Output Port 0 Register (08h) with the values for the LEDs to turn them on or off.
Attach the schematic of your module board, so that I may assist you in getting the slave address.
However, now iam able to communicate with the Cypress from my Atmel Controller.
These steps i followed.
Selecting the SLAVE address as 0x21 for IO expander without read/write bit(since my API is taking care of R/W bits).
Next i wrote Register address 0x08 , to select Port 0 , and followed by 0x00 to make all pins Low , to blink the LEDs.
For reading also i taken 0x2e register , the device ID of Cypress 0x60h.
Atmel studio provided the Ready APIs to make my work easier, It is important to understand the APIs design.
Thanks & Regards,