I use PCA9698 to solve the problem of insufficient IO port.
But there are problems in the use process：
I use the IO of pca9698 to control the digital switch（ADG1612），when the control port of the digital switch is not connected to the IO port of pca9698，i can control the IO as i want.
But when more than 4 control ports of the digital switch are connected to the IO port of pca9698（these ports is in one register），and IO is configured as output,if set these ports(more than 4 ports) HIGH at same time，Configuration registers corresponding to these ports will be configure as input. In this case, it is invalid to configure IO as output.