Some slave serial devices automatically increment their internal address pointer after each byte is clocked by the master. This allows the master to sequentially access multiple registers without resending the write or read command. Other slave devices do not automatically increment their internal address pointer. The MCP23X08 and 17 families of devices have the ability to do either by configuring a control bit. On power-up, the device may be quickly configured by sequentially writing to all of the registers. During normal operation, it may be desirable to turn off the automatic address incrementing so the I/O port can be continually written or read. When the MCP23X17 is in 16-bit mode and the address incrementing is turned off, the address pointer actually points to the two paired registers in a ping-pong manner. For example, the address will alternate between GPIOA and GPIOB if reading the port.